Filed Pursuant to Rule 424(b)(2)
                                                Registration No. 333-87034

PROSPECTUS                                           MERCK STOCK INVESTMENT PLAN


         The Merck Stock Investment Plan (the "Plan") of Merck & Co., Inc., a
New Jersey corporation ("Merck"), provides participants with a convenient and
economical method of purchasing shares of Merck's common stock, $0.01 Par Value
per share ("Common Stock"), and reinvesting cash dividends paid on Common Stock
in additional shares of Common Stock. Participation in the Plan is open to any
registered holder of Common Stock and to any person who becomes a registered
holder of Common Stock by enrolling in the Plan, paying a one-time account
set-up fee of $5 and either making an initial investment of at least $350 or
authorizing automatic monthly cash investments of at least $50. Beneficial
owners of Common Stock whose only shares are registered in names other than
their own (e.g., held in street name in a brokerage account) are not eligible
until they become stockholders of record either by withdrawing the shares from
their brokerage account and registering the shares in their own name or by
enrolling in the Plan in the same manner as a non-stockholder.

         Participants in the Plan may elect to have the cash dividends paid on
all or a percentage of their shares of Common Stock automatically reinvested in
additional shares of Common Stock. Participants may also purchase additional
shares of Common Stock by making optional cash investments in accordance with
the provisions of the Plan. Holders of Common Stock who choose not to
participate in the Plan will continue to receive cash dividends on shares of
Common Stock registered in their name, as declared, by check or direct deposit.

         Shares of Common Stock purchased by participants in the Plan may be
treasury or new issue Common Stock or, at Merck's option, Common Stock purchased
in the open market or in negotiated transactions. Treasury or new issue Common
Stock is purchased from Merck at the market price on the applicable investment
date. The price of Common Stock purchased in the open market or in negotiated
transactions is the weighted average price at which the shares are actually
purchased.

         The Plan supersedes the Merck & Co., Inc. Automatic Dividend
Reinvestment and Cash Payment Plan in its entirety. A complete description of
the Plan begins on page 4 of this Prospectus.


         Shares of Common Stock offered under the Plan to persons who are not
currently stockholders of Merck are offered through Wells Fargo Brokerage
Services, LLC, a registered broker/dealer.

         PLEASE READ THIS PROSPECTUS CAREFULLY BEFORE INVESTING AND RETAIN IT
FOR YOUR FUTURE REFERENCE.

                            ------------------------

THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES AND
EXCHANGE COMMISSION NOR HAS THE SECURITIES AND EXCHANGE COMMISSION PASSED UPON
THE ACCURACY OR ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY
IS A CRIMINAL OFFENSE.

                            ------------------------

          The date of this Prospectus is April 30, 2002.





                              AVAILABLE INFORMATION

        Merck is subject to the informational requirements of the Securities
Exchange Act of 1934, as amended (the "Exchange Act"), and in accordance
therewith files reports, proxy statements and other information with the
Securities and Exchange Commission (the "Commission"). The reports, proxy
statements and other information filed by Merck with the Commission can be
inspected and copied at the Public Reference Room of the Commission at 450 Fifth
Street, NW, Washington, DC 20549 or by calling the Commission at 1-800-SEC-0330.
Such materials also may be accessed through the Commission's Internet Web site
located at http://www.sec.gov. Copies of such materials can be obtained at
prescribed rates by writing to the Commission, Public Reference Section, 450
Fifth Street, NW, Washington, DC 20549.

         Merck has filed a registration statement on Form S-3 (File
No. 333-87034) (the "Registration Statement") with the Commission
registering under the Securities Act of 1933, as amended (the "Securities Act"),
the shares of Common Stock offered hereby. This Prospectus does not contain all
of the information set forth in the Registration Statement and the exhibits
thereto. A copy of the Registration Statement may be inspected or obtained in
the manner described above. Certain portions of the Registration Statement have
been omitted pursuant to the rules and regulations of the Commission. Reference
is hereby made to such omitted portions for further information with respect to
Merck and the shares of Common Stock offered hereby. Statements contained herein
concerning the provisions of certain documents are necessarily summaries of such
documents, and each statement is qualified in its entirety by reference to the
copy of the applicable document filed with the Commission.

                 INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

        The following document filed by Merck with the Commission (File No.
1-3305) pursuant to the Exchange Act is incorporated by reference in this
Prospectus: (a) Annual Report on Form 10-K for the fiscal year ended December
31, 2001.

         All documents filed by Merck with the Commission pursuant to Sections
13(a), 13(c), 14, or 15(d) of the Exchange Act after the date of this Prospectus
and prior to termination of this offering shall be deemed to be incorporated by
reference herein and to be a part hereof from the date of such filing. Any
statement contained in a document incorporated or deemed to be incorporated by
reference herein shall be deemed to be modified or superseded for purposes
hereof to the extent that a statement contained herein or in any other
subsequently filed document that also is, or is deemed to be, incorporated by
reference herein modifies or supersedes such statement. Any such statement so
modified or superseded shall not be deemed, except as so modified or superseded,
to constitute a part of this Prospectus.

         Merck will provide without charge to each person to whom this
Prospectus is delivered (including any beneficial owner of shares of Common
Stock), on the request of such person, a copy of the foregoing document
incorporated herein by reference (other than certain exhibits to such
document). Written or telephone requests should be directed to the Corporate
Secretary, Merck & Co., Inc., One Merck Drive, Whitehouse Station, NJ
08889-0100, telephone (908) 423-1000.


                                       2

                                      MERCK

      Merck & Co., Inc. (the "Company") is a global research-driven
pharmaceutical company that discovers, develops, manufactures and markets a
broad range of human and animal health products, directly and through its joint
ventures, and provides pharmaceutical benefit services through Merck-Medco
Managed Care, L.L.C. ("Merck-Medco"). The Company's operations are principally
managed on a products and services basis and are comprised of two reportable
segments: Merck Pharmaceutical, which includes products marketed either directly
or through joint ventures, and Merck-Medco. Merck Pharmaceutical products
consist of therapeutic and preventive agents, sold by prescription, for the
treatment of human disorders. Merck-Medco revenues are derived from the filling
and management of prescriptions and health management programs.

      The following table shows the sales of various categories of the Company's
products and services:



                 ($ in millions)                    2001          2000          1999
                 ---------------               ---------     ---------     ---------
                                                                  
      Atherosclerosis ....................     $ 7,179.6     $ 5,805.2     $ 5,093.2
      Hypertension/heart failure .........       4,255.6       4,629.1       4,563.8
      Anti-inflammatory/analgesics .......       2,630.5       2,251.7         578.5
      Osteoporosis .......................       1,759.2       1,275.3       1,043.1
      Respiratory ........................       1,375.7         862.2         501.8
      Vaccines/biologicals ...............       1,022.4         952.0         860.0
      Anti-bacterial/anti-fungal .........         795.4         783.3         772.3
      Ophthalmologicals ..................         672.2         656.2         670.0
      Human immunodeficiency virus ("HIV")         411.0         528.8         664.4
      Anti-ulcerants .....................         354.2         849.4         913.9
      Other Merck products ...............         891.2       1,629.7       1,820.6
      Merck-Medco ........................      26,368.7      20,140.3      15,232.4
                                               ---------     ---------     ---------
           Total .........................     $47,715.7     $40,363.2     $32,714.0
                                               =========     =========     =========


      Human health products include therapeutic and preventive agents, generally
sold by prescription, for the treatment of human disorders. Among these are
atherosclerosis products, which include Zocor (simvastatin) and Mevacor
(lovastatin); hypertension/heart failure products, which include Cozaar
(losartan potassium), Hyzaar (losartan potassium and hydrochlorothiazide),
Prinivil (lisinopril), Vasotec (enalapril maleate) and Vaseretic (enalapril
maleate and hydrochlorothiazide); anti-inflammatory/analgesics, of which Vioxx
(rofecoxib), an agent that specifically inhibits COX-2, is the largest-selling;
an osteoporosis product, Fosamax (alendronate sodium), for treatment and
prevention of osteoporosis; a respiratory product, Singulair (montelukast
sodium), a leukotriene receptor antagonist; vaccines/biologicals, of which M-M-R
II (measles, mumps and rubella virus vaccine live), Varivax (varicella virus
vaccine live), a live virus vaccine for the prevention of chickenpox, and
Recombivax HB (hepatitis B vaccine [recombinant]) are the largest-selling;
anti-bacterial/anti-fungal products, of which Primaxin (imipenem and cilastatin
sodium), Noroxin (norfloxacin) and Cancidas (caspofungin acetate) are the
largest-selling; ophthalmologicals, of which Timoptic (timolol maleate),
Timoptic-XE (timolol maleate ophthalmic gel forming solution), Trusopt
(dorzolamide hydrochloride ophthalmic solution) and Cosopt (dorzolamide
hydrochloride and timolol maleate ophthalmic solution) are the largest selling;
HIV products, which include Crixivan (indinavir sulfate), a protease inhibitor
for the treatment of human immunodeficiency viral infection in adults; and
anti-ulcerants, which include Pepcid (famotidine).

      Other Merck products include sales of Proscar (finasteride), which
provides for the treatment of symptomatic benign prostatic hyperplasia in men
with enlarged prostates, Maxalt (rizatriptan benzoate), an anti-migraine
treatment, Propecia (finasteride), which treats male pattern hair loss and
Aggrastat (tirofiban hydrochloride), a platelet blocker for treatment of acute
coronary syndrome, and other human pharmaceuticals; continuing sales to divested
businesses; pharmaceutical and animal health supply sales to the Company's joint
ventures; and supply sales to AstraZeneca LP. Also included in this category are
rebates and discounts on the Company's pharmaceutical products.

      Merck-Medco primarily includes Merck-Medco sales of non-Merck products and
Merck-Medco pharmaceutical benefit services, principally sales of prescription
drugs through managed prescription drug programs, as well as services provided
through programs to manage patient health and drug utilization.

      In January 2002, the Company announced plans to establish Merck-Medco as
a seperate, publicly-traded company. The Company plans an initial public
offering of a portion of the new company by mid-2002, subject to market
conditions. Alternatives for the distribution of the remaining shares in the
new company are under evaluation. The full separation of Merck-Medco should be
completed within 12 months of the initial public offering, subject to receipt
of an Internal Revenue Service ruling that such an event would be tax-free to
shareholders and to other customary conditions.

      Merck provides a more detailed description of its current business and
industry segments, including an overview of the regulatory environment within
which it and its sudsidiaries operate, in its annual report on Form 10-K filed
with the Commission and incorporated by reference herein. A copy of Merck's
most recent annual report on Form 10-K can be obtained without charge. See
"INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE."


                                       3

                             DESCRIPTION OF THE PLAN


PURPOSES

     The Plan provides participants with a convenient and economical method of
systematically increasing their ownership interest in Merck through purchases of
Common Stock and the reinvestment of cash dividends in additional shares of
Common Stock.

COMMENCEMENT

     The Plan has been effective since February 1, 1997. Any funds received
prior to that time will be held for investment until the next purchase date
which is expected to be in the first week of February.

FEATURES

     The Plan has the following features:

         -        Open to Non-Stockholders. Persons who do not currently own
                  shares of Common Stock may become participants in the Plan by
                  paying an account set-up fee of $5 and either making an
                  initial investment of at least $350 or authorizing automatic
                  monthly cash investments of at least $50.

         -        Automatic Reinvestment of Dividends. Cash dividends paid on
                  all or a specified percentage of shares of Common Stock are
                  automatically reinvested in additional shares of Common Stock.

         -        Optional Cash Investments. Participants may make optional cash
                  investments in Common Stock of a minimum of $50 per investment
                  up to an aggregate of $50,000 per year. Optional cash
                  investments may be made by automatic monthly electronic funds
                  transfer or by check or money order at weekly or less frequent
                  intervals, as the participant desires.

         -        Full Investment of Plan Funds. Funds invested in the Plan are
                  fully invested through the purchase of fractional shares, as
                  well as full shares. Cash dividends on fractional shares are
                  reinvested in additional shares of Common Stock.

         -        Telephone Transactions. Participants may establish telephone
                  privileges for their Plan accounts, enabling them to execute
                  certain Plan orders by phone as follows:

                           --       Sell a portion or all of their Plan shares
                                    (If current market value of shares to be
                                    sold is $25,000 or less)

                           --       Request a certificate for a portion or all
                                    of their full Plan shares

                           --       Change the amount of their monthly
                                    Electronic Funds Transfer

                           --       Terminate their monthly Electronic Funds
                                    Transfer

                           --       Change their reinvestment option. (Example:
                                    Change from full reinvestment to partial
                                    reinvestment)

         If you already participate in the Plan and want to receive a form to
establish telephone transaction privileges for your account, please call the
Plan Administrator at (800) 522-9114.

         -        Share Safekeeping. Participants may deposit for safekeeping
                  certificates representing shares of Common Stock held in
                  certificate form, whether or not the shares were issued under
                  the Plan, at no cost to the participants.

         -        Account Statements. Account statements detailing each
                  participant's Plan activities are mailed to each participant
                  on a quarterly basis and following each Plan transaction.



                                      4

CONSIDERATIONS

     You should consider the following prior to participating in the Plan:

     -    Brokerage Commissions. Participants pay a brokerage commission of
          $0.01 for each share of Common Stock purchased or sold for their Plan
          account in open market transactions. Merck expects that generally all
          Plan purchases and sales will be effected in open market transactions.

     -    Service Fees. Participants also pay a service fee as described herein
          for certain Plan transactions, including dividend reinvestment and
          optional cash investments, whether or not the transactions are
          effected in open market transactions.

     -    Investment Timing; Price Risks. Because the prices at which Plan
          shares are purchased are determined as of specified dates or as of
          dates otherwise beyond the control of participants, participants may
          lose certain advantages otherwise available from being able to select
          the timing of their investment. For example, because the price charged
          to participants for shares purchased in the open market or in
          negotiated transactions is the weighted average price at which the
          shares are actually purchased over a period of up to 5 business days
          following an investment date, participants may pay a higher price for
          shares purchased under the Plan than for shares purchased on the
          investment date outside of the Plan.

     -    No Interest Pending Investment. No interest is paid on optional cash
          investments pending their investment in Common Stock.



                                      5

ADMINISTRATION

     As of the date of this Prospectus, administration of the Plan, which
includes enrolling new participants in the Plan, reinvesting dividends,
processing optional cash investments, processing share sale requests, depositing
and safekeeping Plan shares, processing requests for certificates, and issuing
account statements, is handled by Wells Fargo Shareowner Services(SM) (the "Plan
Administrator"). All inquiries and notices (including change of address)
concerning your Plan account are handled by Merck and should be directed to:

              Merck & Co., Inc.
              Stockholder Services Department
              P.O. Box 100 (WS 3AB-40)
              Whitehouse Station, NJ 08889-0100

or by telephone at (800) 613-2104 Monday through Friday, between the hours of
8:30 a.m. and 4:00 p.m., Eastern Standard Time.

     Participants may submit enrollment applications, certificate deposits for
safekeeping, certificate withdrawal, and share sale requests to the Plan
Administrator at the following address:

              Merck & Co., Inc.
              c/o Shareowner Services
              P.O. Box 64855
              St. Paul, MN 55164-0855

     Participants may submit optional cash payments to the following address:

              Shareowner Services
              Dept. 29
              Denver, CO 80281-0029

Shareowner Services can be contacted at (800) 522-9114 between 7:00 a.m. and
7:00 p.m., Central Standard Time, on any business day. Written communications
may also be sent to the Plan Administrator by telefax at (651) 552-6999.

     The Plan Administrator is also responsible for purchasing and selling
shares of Common Stock for participants' Plan accounts, including the selection
of the broker or dealer through which Plan purchases and sales are made. Merck
has no control over the times or prices at which the Plan Administrator effects
transactions in the open market or the selection of the broker or dealer used by
the Plan Administrator to effect open market transactions.

FORMS

     PLAN AUTHORIZATION FORM. A Plan Authorization Form is used to enroll in the
Plan and, at the time of enrollment, authorize electronic funds transfers and
telephone transaction privileges.

     PLAN TRANSACTION FORM. A Plan Transaction Form is used to make optional
cash investments, transfer or sell your Plan shares, deposit your share
certificates with the Plan Administrator (if done after enrollment), and
terminate your participation in the Plan. A Plan Transaction Form is attached to
each account statement mailed to participants.

     ACCOUNT ELECTION FORM. An Account Election Form is used to authorize
electronic funds transfers after enrollment or to change the amount of or
terminate electronic funds transfers.

     Account Election Forms and additional Plan Authorization Forms and Plan
Transaction Forms can be obtained from the Plan Administrator upon request.

ELIGIBILITY

     Any person or entity, whether or not currently a registered holder of
Common Stock, may participate in the Plan by enrolling in accordance with the
procedures described in "Enrollment and Participation" below. Merck reserves the
right to deny, modify, suspend or terminate participation by any person or
entity. See "Other Information -- Denial or Termination of Participation by
Merck."

ENROLLMENT AND PARTICIPATION

     You may enroll in the Plan at any time by completing a Plan Authorization
Form and returning it to the Plan Administrator at the address set forth on the
form.



                                      6

     EXISTING STOCKHOLDERS.

         EXISTING STOCKHOLDERS. If you are a registered holder of Common Stock
     but not currently participating in the Plan, you must complete a Plan
     Authorization Form to participate in the new Plan. If you are a beneficial
     owner of Common Stock whose only shares are held in names other than your
     own (e.g., held by brokers, trustees or bank nominees), you must complete a
     Plan Authorization Form and either (a) become a stockholder of record by
     having the shares registered in your name, or (b) become a stockholder of
     record by enrolling in the Plan in the same manner as a non-stockholder.

         NON-STOCKHOLDERS. If you are not a registered owner of Common Stock,
     you must complete a Plan Authorization Form and pay a one-time account
     set-up fee of $5 PLUS an optional cash investment fee of $5 for a total of
     $10. You must also make an initial cash investment of at least $350. For
     automatic monthly cash investments, an initial investment of $50, together
     with a one time account set up fee $5 is required. A maximum of $50,000 may
     be initially invested in the Plan.

              EXAMPLE 1: A non-stockholder who wishes to enroll in the Plan by
         making an initial investment would complete the account authorization
         form and submit a check made payable to Shareowner Services for $360.00
         (initial investment of $350 plus $5 one-time enrollment fee and $5
         optional cash investment fee).

              EXAMPLE 2: A non-stockholder who wishes to enroll in the Plan by
         authorizing monthly electronic investments from his savings or checking
         account would complete the account authorization form INCLUDING SECTION
         D (Automatic Cash Withdrawal and Investment) authorizing monthly
         investments of at least $50. The investor would include a check for at
         least $55 to cover the one-time account set-up fee of $5 and the first
         optional cash investment of $50 made payable to Shareowner Services.
         All subsequent monthly optional cash investments will be electronically
         debited from the participant's bank account. All monthly cash purchases
         made by electronic investment will be assessed a $2 transaction fee
         which will be deducted from the cash investment.

                                   INVESTMENTS

     DIVIDEND REINVESTMENT. As described below, by participating in the Plan,
you may have the cash dividends paid on all or a percentage of your shares of
Common Stock (net of brokerage commissions and service fees as described below)
automatically reinvested in Common Stock on the dividend payment date. THE
PAYMENT OF DIVIDENDS ON COMMON STOCK IS AT THE DISCRETION OF MERCK'S BOARD OF
DIRECTORS.

REINVESTMENT OPTIONS

     FULL DIVIDEND REINVESTMENT. If you elect the "Full Dividend Reinvestment"
option on your Plan Authorization Form, the Plan Administrator will reinvest in
additional shares of Common Stock all cash dividends paid on all shares of
Common Stock then or subsequently registered in your name and on all shares of
Common Stock then or subsequently held in your Plan account, including
fractional shares and shares purchased with optional cash investments made under
the Plan.

     PARTIAL DIVIDEND REINVESTMENT. If you elect the "Partial Dividend
Reinvestment" option on your Plan Authorization Form, you must select the
percentage (from 10% to 90%, in increments of 10%) of the total number of shares
of Common Stock then or subsequently registered in your name and then or
subsequently held in your Plan account with respect to which you want cash
dividends reinvested. The Plan Administrator will reinvest in additional shares
of Common Stock all cash dividends paid on the specified percentage of shares.

     OPTIONAL CASH INVESTMENTS ONLY. If you elect the "Optional Cash Investments
Only" option, you will continue to receive, as declared, by check or direct
deposit, cash dividends paid on shares of Common Stock then or subsequently
registered in your name and then or subsequently held in your Plan account.

     DIVIDEND PAYMENT DATES. If your Plan Authorization Form is received by the
Plan Administrator on or before the record date for a particular dividend,
dividend reinvestment will begin with respect to dividends paid on the next
dividend payment date. If your Plan Authorization Form is received by the Plan
Administrator after the record date, dividend reinvestment will not begin until
the dividend payment date following the next record date. Dividends on Common
Stock have historically been paid on the first business day of January, April,
July, and October. Thus, for example, to begin automatic reinvestment of a
dividend expected to be paid on April 1 in a given year, the Plan Administrator
should receive your Plan Authorization Form by the first week in March.



                                      7

CASH INVESTMENTS

     INITIAL CASH INVESTMENT. If you are not a registered owner of Common Stock,
you must include an initial cash investment of at least $350 with your completed
Plan Authorization Form or authorize automatic monthly cash investments by
electronic funds transfer of at least $50. If you include an initial cash
investment with your Plan Authorization Form, you must also include a one-time
account set-up fee of $5 plus an optional cash investment fee of $5. If you
elect to sign up for automatic monthly cash investments of at least $50, you
must include at least $50 to cover the first initial investment along with a
one-time set-up fee of $5. Subsequent electronic cash investments will be
assessed a $2 transaction fee which will be deducted from the investment amount.
See "Enrollment and Participation" above. Initial cash investments and payment
of the account set-up fee must be made by check or money order payable to "Wells
Fargo Shareowner Services" in U.S. funds.

     OPTIONAL CASH INVESTMENTS. Participants may make optional cash investments
at any time by personal check, money order or electronic funds transfer from a
designated U.S. bank account. Participants may vary their optional cash
investments from a minimum of $50 per investment up to a maximum of $50,000 per
year. Initial cash investments are included in the month in which they are made
for purposes of determining whether the $50,000 maximum has been reached.

     INITIAL AND OPTIONAL CASH INVESTMENTS ARE INVESTED IN SHARES OF COMMON
STOCK NET OF BROKERAGE COMMISSIONS AND SERVICE FEES AS DESCRIBED BELOW.

     CHECK OR MONEY ORDER. Optional cash investments made by check or money
order must be accompanied by a completed Plan Transaction Form. The Plan
Administrator will make every effort to process your cash investment for the
next investment date, provided that the funds are received by the Plan
Administrator no later than two business days prior to the investment date for
an initial cash investment and one business day prior to an investment date for
optional cash payments. Otherwise, cash investments are held by the Plan
Administrator for investment on the next investment date. (See definition of
Cash Investments, above.) Cash investments made by check or money order must be
payable to "Wells Fargo Shareowner Services" in U.S. funds. The Plan
Administrator will not be liable for any claim arising out of failure to
purchase stock on a certain date or at a specific price. This risk should be
evaluated by the participant and is a risk that is borne solely by the
participant.

     ELECTRONIC FUNDS TRANSFER. In addition to making optional cash investments
by check or money order, participants may authorize automatic monthly electronic
funds transfers from designated bank accounts. Participants' bank accounts are
debited 4 business days prior to the investment date which is generally the
third Tuesday or, if the third Tuesday is not a business day, the business day
next following the third Tuesday of each month. Participants do not receive any
confirmation of the transfer of funds other than as reflected in their monthly
Plan account statements and in their bank account statements.

     To authorize electronic funds transfers, complete and sign the automatic
funds transfer section of the Plan Authorization Form and return it to the Plan
Administrator together with a voided blank check or deposit slip for the account
from which funds are to be transferred. Your automatic funds transfers will
begin as soon as practicable after the Plan Administrator receives the
authorization form. You may change the amount of your monthly transfer or
terminate your monthly transfer altogether by completing an EFT Authorization
Form and returning it to the Plan Administrator or by contacting the Plan
Administrator toll free at (800) 522-9114. To be effective with respect to a
particular investment date, your change or termination request must be received
by the Plan Administrator at least fifteen business days prior to the investment
date.

INVESTMENT DATES

     DIVIDEND REINVESTMENT. Cash dividends are expected to be reinvested on the
applicable dividend payment date or, if the dividend payment date is not a
business day, the business day next following the dividend payment date.

     INITIAL AND OPTIONAL CASH INVESTMENTS. Initial and optional cash
investments are expected to be made on (a) Tuesday of each week or, if Tuesday
is not a business day, the business day next following Tuesday or (b) in any
week in which a cash dividend is paid, the dividend payment date or, if the
dividend payment date is not a business day, the business day next following the
dividend payment date.

     NO INTEREST IS PAID ON FUNDS HELD BY THE PLAN ADMINISTRATOR PENDING THEIR
INVESTMENT IN COMMON STOCK. ALL OPTIONAL CASH INVESTMENTS, INCLUDING THE INITIAL
CASH INVESTMENT, ARE SUBJECT TO THE COLLECTION BY THE PLAN ADMINISTRATOR OF FULL
FACE VALUE IN U.S. FUNDS.



                                      8

     SOURCE OF SHARES. Shares purchased by participants under the Plan are
acquired in the open market, negotiated transactions or purchased from treasury
or new issue Common Stock that Merck has registered under the Securities Act.
The Plan Administrator purchases shares in the open market or in negotiated
transactions as soon as practicable (but in no event more than 5 business days)
after the applicable investment date, subject to any waiting periods required
under applicable securities laws or stock exchange regulations. Merck determines
the source or sources of shares used to fulfill Plan requirements and, subject
to certain regulatory restrictions on the frequency with which it can change its
determination, may change such determination from time to time without notice to
Plan participants. Merck expects that generally all Plan purchases will be
effected in open market transactions.

     PRICE OF SHARES. The price per share of treasury or new issue Common Stock
is the average of the high and low sale prices of the Common Stock (as reported
on the New York Stock Exchange Composite Tape) on the applicable investment date
or, if the New York Stock Exchange is closed on the investment date, on the next
preceding day the New York Stock Exchange is open. The price of shares purchased
in the open market or in negotiated transactions is the weighted average price
at which the shares are actually purchased for the applicable investment date.
All purchases will be made within 5 business days of an investment date. The
Plan Administrator may in its discretion commingle participants' funds for the
purpose of effecting purchase orders and may offset purchase and sale orders to
arrive at a net purchase or sale order. Because the prices at which shares are
purchased under the Plan are determined as of specified dates or as of dates
otherwise beyond the control of participants, participants may lose any
advantage otherwise available from being able to select the timing of their
investment.

BROKERAGE COMMISSIONS, SERVICE FEES AND OTHER COSTS

     ACCOUNT SET-UP. Persons who are not registered holders of Common Stock,
including persons authorizing automatic monthly cash investments, are charged a
one-time account set-up fee of $5. Please note: As mentioned earlier in this
prospectus, an optional cash investment transaction fee of $5 will be assessed
on all initial investments made by check or money order. The fee must be paid by
check or money order and is due at the time of enrollment. The fees must be
added to the minimum initial cash investment of $350. A $2 per cash investment
fee is assessed on all monthly optional cash investments made by electronic bank
transfer.

     BROKERAGE COMMISSIONS. In addition to the service fees discussed below,
participants pay a brokerage commission of $0.01 for each share of Common Stock
purchased or sold for their Plan account in open market transactions, even if a
purchase or sale order is used to offset another Plan order. Merck expects that
generally all Plan purchases and sales will be effected in open market
transactions. Brokerage commissions payable with respect to Plan purchases are
deducted from the amount invested on behalf of participants. Brokerage
commissions payable with respect to Plan sales are deducted from the proceeds
payable to participants.

     SERVICE FEES. For each dividend reinvestment transaction, participants pay
a service fee equal to 4% of the cash dividend reinvested up to a maximum of $2
per transaction. For each optional cash investment made by check or money order,
participants pay a service fee of $5, and for each optional cash investment made
by automatic electronic funds transfer, participants pay a service fee of $2.
Dividend reinvestment and optional cash investment service fees are in addition
to brokerage commissions and are deducted from the amount invested on behalf of
participants. Participants pay a service fee of $5 in connection with sales of
Plan shares. The service fee is in addition to brokerage commissions and is
deducted from the proceeds payable to the selling participant.

     COMMISSIONS AND FEES SUBJECT TO CHANGE. The Plan Administrator may change
from time to time the amount of commissions and fees charged participants upon
30 days' prior notice to participants.

ACCOUNT STATEMENTS

     The Plan Administrator maintains an account for each Plan participant and
sends account statements to each participant as soon as practicable after each
quarterly dividend reinvestment and each weekly optional cash investment and
after any transfer, sale or withdrawal of Plan shares. The account statements
provide participants with records of their purchases and sales and should be
retained for tax purposes.

SHARE CERTIFICATES

     Plan purchases are credited to each participant's account and shown on the
participant's account statement. Participants do not receive certificates for
their Plan shares unless requested. This protects against loss, theft or
destruction of stock certificates and reduces Merck's administrative costs
associated with the Plan. Participants may obtain certificates for some or all
full Plan shares at any time by submitting a Plan Transaction Form to the Plan
Administrator or contacting the Plan Administrator toll free at (800) 522-9114.
Any remaining full and fractional



                                      9

shares continue to be credited to participants' accounts. Certificates for
fractional shares are not issued under any conditions.

SHARE SAFEKEEPING

     At any time beginning with enrollment in the Plan, participants may deposit
with the Plan Administrator certificates representing shares of Common Stock,
whether or not the shares were acquired under the Plan, at no cost to
participants. To use this service, participants must send their certificates to
the Plan Administrator with a properly completed Plan Transaction Form. Shares
represented by certificates deposited with the Plan Administrator are credited
to participants' accounts and thereafter are treated as if acquired under the
Plan. Participants are responsible for maintaining their own records of the cost
basis of certificated shares deposited with the Plan Administrator. Beneficial
owners of Common Stock registered in street or other nominee name may in certain
cases be able to electronically transfer their shares from their existing
account to a Plan account. Beneficial owners who want to take advantage of this
service should contact the Plan Administrator to obtain transfer instructions.

     Merck strongly recommends that participants use registered mail to mail
their certificates to the Plan Administrator, insuring the certificates for 2%
of the current market value of the shares represented thereby. In any case,
participants bear the full risk of loss, regardless of the method used, in the
event the certificates are lost.

      PARTICIPANTS SHOULD NOT ENDORSE THEIR CERTIFICATES PRIOR TO MAILING.

SHARE TRANSFERS WITHIN PLAN

     Participants may purchase shares of Common Stock for others by making cash
investments on their behalf. To do this, you need only complete a Plan
Authorization Form in the name of the recipient and return the completed form to
the Plan Administrator together with the one-time account set-up fee of $5, a $5
optional cash investment fee (not required for automatic monthly cash
investments) and either an initial investment of at least $350 or an
authorization for automatic monthly cash investments of at least $50.

     Plan shares also may be transferred to a Plan account of another person
subject to compliance with any applicable laws. To do this, participants must
complete a Plan Transaction Form and return the completed Plan Transaction Form,
together with an executed stock assignment, to the Plan Administrator. The
signature of the transferring participant on the stock assignment must be
Medallion guaranteed by an eligible financial institution. Stock assignments can
be obtained from the Plan Administrator. If the person to whom the shares are
gifted or transferred is not a participant in the Plan, the Plan Administrator
will automatically open an account for the person and enroll him or her in the
Plan.

     Participants may not pledge or grant a security interest in Plan shares or
transfer Plan shares outside of the Plan unless certificates representing the
shares have been issued by the Plan Administrator.

SALE OF SHARES

     Participants may sell some or all of their Plan shares by submitting the
appropriate information on the Plan Transaction Form or by submitting a written
request to the Plan Administrator. If the current market value of the shares
requested to be sold is $25,000 or less, and the participant has previously
authorized telephone transactions, a participant may sell Plan shares by
contacting the Plan Administrator toll free at (800) 522-9114. The Plan
Administrator may match or offset participants' sales orders against one or more
purchase orders of other participants in the Plan. If not offset, the Plan
Administrator executes the order on behalf of the participant in the open market
or in negotiated transactions. The Plan Administrator may sell Plan shares to
Merck. After settlement of the sale, the Plan Administrator will send the
participant a check for the net proceeds of the sale. The proceeds received by
the participant are based on the weighted average price at which the shares were
sold less brokerage commissions, service fees charged by the Plan Administrator,
and applicable transfer taxes.

     THE PLAN ADMINISTRATOR WILL MAKE EVERY EFFORT TO PROCESS YOUR SALE ORDER ON
THE NEXT BUSINESS DAY FOLLOWING RECEIPT OF YOUR PROPERLY COMPLETED REQUEST,
PROVIDED THAT INSTRUCTIONS ARE RECEIVED BEFORE 5:00 P.M. CST (SALE REQUESTS
INVOLVING MULTIPLE TRANSACTIONS MAY EXPERIENCE A DELAY). THE PLAN ADMINISTRATOR
WILL NOT BE LIABLE FOR ANY CLAIM ARISING OUT OF FAILURE TO SELL STOCK ON A
CERTAIN DATE OR AT A SPECIFIC PRICE. THIS RISK SHOULD BE EVALUATED BY THE
PARTICIPANT AND IS A RISK THAT IS BORNE SOLELY BY THE PARTICIPANT.

TERMINATION

     Participants may terminate their participation in the Plan by submitting
the appropriate information on a Plan Transaction Form or by submitting a
written request to the Plan Administrator. If the current market value of a



                                      10

participant's Plan account is $25,000 or less, and the participant has
previously authorized telephone transactions, a participant may terminate his or
her participation in the Plan by contacting the Plan Administrator toll free at
(800) 522-9114. Termination requests must be received by the Plan Administrator
three days prior to the record date to be effective as to the next cash
dividend. Any such notice received after a dividend record date shall not be
effective until dividends paid for such record date have been credited to the
participant's account. If a participant sends notice of termination or a request
to sell to the Plan Administrator between the record date and the payable date
for a stock distribution, the request will not be processed until the stock
distribution is credited to the participant's account. In addition, termination
requests of participants making optional cash investments by electronic funds
transfers must be received by the Plan Administrator at least 15 business days
prior to the scheduled investment date to ensure that the request is effective
as to the next optional cash investment.

     Upon termination of a participant's participation in the Plan, unless the
participant has requested on the Plan Transaction Form that some or all Plan
shares be sold, the Plan Administrator will send the participant a certificate
representing the number of full shares in the participant's Plan account and a
check in the amount of the market value of any fractional share. If a
participant so requests on the Plan Transaction Form, the Plan Administrator
will sell some or all Plan shares on behalf of the participant. After settlement
of the sale, the Plan Administrator will send the participant a check in the
amount of the net proceeds of the sale (plus the market value of any fractional
Plan share) and a certificate representing any full Plan shares not sold. The
net proceeds received by the participant are based on the weighted average price
at which the shares were sold less brokerage commissions of $ .01 per share, a
$5 sale fee charged by the Plan Administrator, and applicable transfer taxes.

     After termination, previous participants may re-enroll in the Plan by
submitting a new Plan Authorization Form and complying with all other enrollment
procedures (see "Enrollment and Participation"). In order to minimize
unnecessary Plan administrative costs and to encourage use of the Plan as a
long-term investment vehicle, Merck reserves the right to deny participation in
the Plan to previous participants who Merck or the Plan Administrator believes
have been excessive in their enrollment and termination.

OTHER INFORMATION

     STOCK DIVIDENDS AND STOCK SPLITS. Any shares distributable to a Plan
participant pursuant to a stock dividend or stock split by Merck on shares
registered in the name of or credited to the account of a Participant under the
Plan will be added to the Participant's account and not mailed or delivered
directly to the Participant. The Participant, however, may request Merck to
issue certificates for such stock dividends or split shares once they are added
to the Participant's account (see "Share Certificates" page 9). If a
participant sends notice of termination or a request to sell to the Plan
Administrator between the record date and the payable date for a stock
distribution, the request will not be processed until the stock distribution is
credited to the participant's account.

     DIVIDEND AND VOTING RIGHTS. Dividend and voting rights of shares purchased
under the Plan commence upon settlement of the transaction, which normally is
three business days after purchase. Shares of Common Stock purchased on or
within two business days prior to a dividend record date are considered
"ex-dividend" and therefore not entitled to payment of that dividend.

     VOTING OF PLAN SHARES. For each meeting of stockholders, participants
receive proxy materials that allow them to vote their Plan shares by proxy.
Alternatively, participants can elect to vote their Plan shares in person at the
meeting.

     LIMITATION OF LIABILITY. In administering the Plan, neither Wells Fargo,
the Plan Administrator nor the Independent Agent is liable for any good faith
act or omission to act, including but not limited to any claim of liability (a)
arising out of the failure to terminate a participant's account upon such
participant's death prior to receipt of notice in writing of such death, (b)
with respect to the prices or times at which shares are purchased or sold, or
(c) as to the value of the shares acquired for participants. Merck reserves the
right to interpret and regulate the Plan as it deems necessary or advisable in
connection with the Plan's operations.

     MODIFICATION OR TERMINATION OF THE PLAN. Merck may suspend, modify or
terminate the Plan at any time in whole or in part or with respect to
participants in certain jurisdictions. Notice of such suspension, modification
or termination will be sent to all affected participants. No such event will
affect any shares then credited to a participant's account. Upon any whole or
partial termination of the Plan by Wells Fargo, each affected participant will
receive a certificate for all full Plan shares and a check in the amount of the
market value of any fractional Plan share.

     DENIAL OR TERMINATION OF PARTICIPATION BY WELLS FARGO. At the direction of
Wells Fargo, the Plan Administrator may terminate a participant's participation
in the



                                      11

Plan if the participant does not own at least one full share in the
participant's name or held through the Plan. Merck also reserves the right to
deny, modify, suspend or terminate participation in the Plan by otherwise
eligible persons to the extent Merck deems it advisable or necessary in its
discretion to comply with applicable laws or to eliminate practices that are not
consistent with the purposes of the Plan. Participants whose participation in
the Plan is terminated will receive certificates for all full Plan shares and a
check in the amount of the market value of any fractional Plan share.

                         FEDERAL INCOME TAX INFORMATION


     THE INFORMATION SET FORTH BELOW SUMMARIZES CERTAIN FEDERAL INCOME TAX
CONSEQUENCES OF PARTICIPATION IN THE PLAN. THE INFORMATION IS NOT INTENDED TO BE
A COMPLETE DESCRIPTION OF ALL SUCH CONSEQUENCES, NOR IS IT INTENDED TO BE A
DESCRIPTION OF ANY KIND OF THE STATE, LOCAL OR FOREIGN TAX CONSEQUENCES OF
PARTICIPATION IN THE PLAN. THE DESCRIPTION OF FEDERAL INCOME TAX CONSEQUENCES
MAY BE AFFECTED BY FUTURE LEGISLATION, IRS RULINGS AND REGULATIONS AND/OR COURT
DECISIONS. FOR THAT REASON, PARTICIPANTS SHOULD CONSULT THEIR OWN TAX ADVISORS
WITH RESPECT TO THE FEDERAL INCOME TAX CONSEQUENCES, AS WELL AS THE STATE, LOCAL
AND FOREIGN INCOME TAX CONSEQUENCES, OF PARTICIPATION IN THE PLAN.

FEDERAL INCOME TAX CONSEQUENCES

     DIVIDEND INCOME. Reinvested dividends are treated for federal income tax
purposes in the same manner as if the participant had received the dividends in
cash on the applicable dividend payment date.

     COST BASIS OF SHARES. For federal income tax purposes, the cost basis of
shares purchased with reinvested dividends or optional cash investments is the
purchase price of the shares.

     GAINS AND LOSSES FROM THE SALE OF SHARES. Participants do not realize any
taxable income from the issuance of certificates representing Plan shares.
Participants may realize gain or loss, however, at the time the shares are sold
by the Independent Agent or by the participants after withdrawal of the shares
from the Plan. The amount of realized gain or loss, if any, is based on the
difference between the amount the participant receives for the shares and the
cost basis of the shares.

     IRS REPORTS. The Plan Administrator reports dividend income to participants
and the IRS on Form 1099-DIV. The Plan Administrator reports the proceeds from
the sale of Plan shares to the selling participants and the IRS on Form 1099-B.

DIVIDENDS SUBJECT TO WITHHOLDING

     A participant's dividends are subject to federal withholding if the
participant fails to provide a taxpayer identification number to the Plan
Administrator. Dividends of participants residing in certain foreign countries
may also be subject to federal withholding. In any case in which federal income
taxes are required to be withheld, the Plan Administrator reinvests an amount
equal to the dividends less the amount of tax withheld. For IRS reporting
purposes, the amount of the dividend withheld is included in the dividend
income.

                                 USE OF PROCEEDS

     The proceeds from the sales of treasury or new issue Common Stock pursuant
to the Plan, if any, would be used for general corporate purposes. Merck has no
basis for estimating either the number of shares of Common Stock that will
ultimately be sold pursuant to the Plan or the prices at which such shares will
be sold. Merck expects that generally all Plan purchases and sales will be
effected in open market transactions.

                                     EXPERTS

     The consolidated financial statements of Merck and subsidiaries as of
December 31, 2001 and 2000, and for each of the years in the three-year period
ended December 31, 2001, incorporated by reference herein, have been
incorporated herein in reliance upon the report of Arthur Andersen, LLP,
independent public accountants, incorporated by reference herein, and upon the
authority of said firm as experts in accounting and auditing.



                                      12

                          SUMMARY OF PLAN SERVICE FEES


                                                                                
Account Set-up..................................................................   $5
  One-time charge for non-stockholders
Optional Cash Investments by check or money order........................          $5
  Fee is assessed on each investment mailed to the administrator -- if
  multiple investments are made for one investment date, a $5 fee will be
  charged for each optional cash investment processed for that investment date.
Optional Cash Investments by electronic funds transfer..........................   $2
Dividend Reinvestment (per dividend reinvested).................................   4% of the dividend to be reinvested
  The fee is deducted from the dividend amount.                                    or $2, whichever is smaller
Sales (full or partial).........................................................   $5
   Fee is assessed for each sale request -- the sale fee and brokerage
  commissions are deducted from the sale proceeds.
Brokerage Commissions...........................................................   $.01 per share purchased or sold
  Brokerage commissions apply to all share purchases and sales, including
  dividend reinvestment.
                                                                                   ***At its discretion, Merck may charge
                                                                                   a fee for researching information
Copies of Prior Year Account Statements.........................................   that is more than one year old.


The following services are provided at no cost to the participant:

-        Certificate withdrawal requests

-        Safekeeping of plan shares

-        Full or partial transfer of plan shares

-        Copies of account statements for the current year



                                      13

                                TABLE OF CONTENTS



Available Information                                                          2
Incorporation of Certain Documents by Reference                                2
Merck                                                                          3
Description of the Plan                                                        4
Purposes                                                                       4
Commencement                                                                   4
Features                                                                       4
Considerations                                                                 5
Administration                                                                 6
Forms                                                                          6
Eligibility                                                                    6
Enrollment and Participation                                                   6
Investments                                                                    7
Brokerage Commissions, Service Fees and Other Costs                            9
Account Statements                                                             9
Share Certificates                                                             9
Share Safekeeping                                                             10
Share Transfers Within Plan                                                   10
Sale of Shares                                                                10
Termination                                                                   10
Other Information                                                             11
Federal Income Tax Information                                                12
Federal Income Tax Consequences                                               12
Dividends Subject to Withholding                                              12
Use of Proceeds                                                               12
Experts                                                                       12
Summary of Plan Services Fees                                                 13


     NEITHER THE DELIVERY OF THIS PROSPECTUS NOR ANY SALES HEREUNDER SHALL UNDER
ANY CIRCUMSTANCES CREATE ANY IMPLICATION THAT THERE HAS BEEN NO CHANGE IN THE
AFFAIRS OF MERCK & CO., INC. ("MERCK") SINCE THE DATE HEREOF. NO DEALER, BROKER,
SALES REPRESENTATIVE OR ANY OTHER PERSON HAS BEEN AUTHORIZED TO GIVE ANY
INFORMATION OR TO MAKE ANY REPRESENTATIONS, OTHER THAN THOSE CONTAINED IN THIS
PROSPECTUS, IN CONNECTION WITH THE OFFERING CONTAINED IN THIS PROSPECTUS, AND
INFORMATION OR REPRESENTATIONS NOT HEREIN CONTAINED, IF GIVEN OR MADE, MUST NOT
BE RELIED UPON AS HAVING BEEN AUTHORIZED BY MERCK. THIS PROSPECTUS DOES NOT
CONSTITUTE AN OFFERING IN ANY STATE OR JURISDICTION IN WHICH SUCH OFFERING MAY
NOT LAWFULLY BE MADE.

                                   PROSPECTUS


                                    [GRAPHIC]


                              STOCK INVESTMENT PLAN



                                       14