<PAGE>   1


AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON MARCH 6, 2000
                                                       REGISTRATION NO. 333-____

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

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                             ----------------------

                                    FORM S-8

            REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933

                               MERCK & CO., INC.
             (Exact Name of Registrant as Specified in its Charter)

<TABLE>
<CAPTION>
                        NEW JERSEY                                                            22-1109110
<S>                                                                             <C>
(State or Other Jurisdiction of Incorporation or Organization)                   (I.R.S. Employer Identification No.)
</TABLE>

                                  P.O. BOX 100
                                ONE MERCK DRIVE
                       WHITEHOUSE STATION, NJ 08889-0100
         (Address, Including Zip Code, of Principal Executive Offices)

                           MERIAL 401(k) SAVINGS PLAN
                            (Full Title of the Plan)

                                CELIA A. COLBERT
            VICE PRESIDENT, SECRETARY AND ASSISTANT GENERAL COUNSEL
                               MERCK & CO., INC.
                                  P.O. BOX 100
                   WHITEHOUSE STATION, NEW JERSEY 08889-0100
                                 (908) 423-1000
           (Name, Address, Including Zip Code, and Telephone Number,
                   Including Area Code, of Agent for Service)

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

                                With a copy to:
                             WARREN J. CASEY, ESQ.
                        PITNEY, HARDIN, KIPP & SZUCH LLP
                                 P.O. BOX 1945
                       MORRISTOWN, NEW JERSEY 07962-1945
                                 (973) 966-6300

                        CALCULATION OF REGISTRATION FEE

<TABLE>
<CAPTION>

        Title of                  Amount             Proposed Maximum        Proposed Maximum            Amount Of
     Securities To                To Be               Offering Price             Aggregate              Registration
     Be Registered              Registered              Per Share             Offering Price                Fee
------------------------- ----------------------- ----------------------- ------------------------ -----------------------
<S>                       <C>                     <C>                     <C>                      <C>
Common Stock (Par Value
$.01 per share)               200,000 (1)                $60.75 (2)          $12,150,000 (2)              $3,207.60

Plan interests related       An indeterminate              N/A                      N/A                     N/A
to Merial Limited             amount of plan
401(k) Savings                interests (3)
Plan............
------------------------- ----------------------- ----------------------- ------------------------ -----------------------
</TABLE>

    (1)  Based on an estimate of the number of shares that will be purchased
         pursuant to the Merial Limited 401(k) Savings Plan. Pursuant to Rule
         416(c) of the Securities Act of 1933, as amended (the "Securities
         Act"), there is also being registered such number of additional shares
         that may become available for purchase pursuant to such plan in the
         event of certain changes in the outstanding shares, including
         reorganizations, mergers, recapitalizations, restructurings, stock
         dividends, stock splits, reverse stock splits and reclassifications.

    (2)  Estimated pursuant to paragraphs (c) and (h) of Rule 457 of the
         Securities Act, solely for the purpose of calculating the registration
         fee, based upon the average of the high and low sales prices of shares
         of Common Stock on March 1, 2000, as reported on the New York
         Stock Exchange.

    (3)  Pursuant to Rule 416 (c) of the Securities Act, this Registration
         Statement covers an indeterminate amount of plan interests to be
         offered or sold pursuant to the Merial Limited 401(k) Savings Plan
         attached as an exhibit hereto.


<PAGE>   2

                                     PART I

              INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

            The document(s) containing the information specified in this Part I
   will be sent or given to employees as specified by Rule 428(b)(1)
   promulgated under the Securities Act. Such documents need not be filed with
   the Securities and Exchange Commission (the "Commission").

                                    PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

   ITEM 3.           INCORPORATION OF DOCUMENTS BY REFERENCE

            The following documents filed by Merck & Co., Inc. (the
   "Registrant") (Exchange Act File No. 1-3305) with the Commission are
   incorporated herein and made a part hereof:

            (a)      Annual Report on Form 10-K, filed on March 24, 1999, for
                     the fiscal year ended December 31, 1998;

            (b)      Proxy Statement for the Annual Meeting of Stockholders
                     held on April 27, 1999, filed on March 18, 1999;

            (c)      Quarterly Report on Form 10-Q, filed on May 12, 1999, for
                     the quarter ended March 31, 1999;

            (d)      Form 10-K/A, filed on June 11, 1999, amending the
                     Registrant's Annual Report on Form 10-K for the fiscal
                     year ended December 31, 1998;

            (e)      Quarterly Report on Form 10-Q, filed on August 12, 1999,
                     for the quarter ended June 30, 1999;

            (f)      Quarterly Report on Form 10-Q, filed on November 12, 1999,
                     for the quarter ended September 30, 1999;

            (g)      Current Report on Form 8-K dated December 9, 1999, filed
                     on December 16, 1999; and

            (h)      The descriptions of the Common Stock of the Registrant set
                     forth in the Registrant's Registration Statements pursuant
                     to Section 12 of the Exchange Act, and any amendment or
                     report filed for the purpose of updating such description.

            All reports or other documents filed by the Registrant pursuant to
   Sections 13, 14 or 15(d) of the Securities Exchange Act of 1934, as amended
   (the "Exchange Act") and prior to the filing of a post-effective amendment
   which indicates that all securities offered have been sold or which
   deregisters all securities then remaining unsold, hereby are incorporated
   herein by reference and shall be deemed a part hereof from the date of
   filing of such documents. An Exhibit Index can be found on page 9 of this
   Registration Statement. 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 of this Registration Statement to the
   extent that a statement contained herein or in any other subsequently filed
   document which 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 Registration Statement.

                                       2

<PAGE>   3


   ITEM 4.           DESCRIPTION OF SECURITIES

                     Not applicable.

   ITEM 5.           INTERESTS OF NAMED EXPERTS AND COUNSEL

           The validity of the Common Stock will be passed upon for the
   Registrant by Celia A. Colbert, Vice President, Secretary & Assistant
   General Counsel of the Company.

   ITEM 6.           INDEMNIFICATION OF DIRECTORS AND OFFICERS

         The New Jersey Business Corporation Act provides that a New Jersey
   corporation has the power to indemnify a director or officer against his or
   her expenses and liabilities in connection with any proceeding involving the
   director or officer by reason of his or her being or having been such a
   director or officer, other than a proceeding by or in the right of the
   corporation, if such a director or officer acted in good faith and in a
   manner he or she reasonably believed to be in or not opposed to the best
   interests of the corporation; and with respect to any criminal proceeding,
   such director or officer had no reasonable cause to believe his or her
   conduct was unlawful.

         The indemnification and advancement of expenses shall not exclude any
   other rights, including the right to be indemnified against liabilities and
   expenses incurred in proceedings by or in the right of the corporation, to
   which a director or officer may be entitled under a certificate of
   incorporation, bylaw, agreement, vote of shareholders, or otherwise;
   provided that no indemnification shall be made to or on behalf of a director
   or officer if a judgment or other final adjudication adverse to the director
   or officer establishes that his or her acts or omissions (a) were in breach
   of his or her duty of loyalty to the corporation or its shareholders, (b)
   were not in good faith or involved a knowing violation of law or (c)
   resulted in receipt by the director or officer of an improper personal
   benefit.

         The Registrant's Restated Certificate of Incorporation provides that,
   to the fullest extent permitted by the laws of the State of New Jersey,
   directors and officers of the Registrant shall not be personally liable to
   the Registrant or its stockholders for damages for breach of any duty owed
   to the Registrant or its stockholders, except that a director or officer
   shall not be relieved from liability for any breach of duty based upon an
   act or omission (a) in breach of such person's duty of loyalty to the
   Registrant or its stockholders, (b) not in good faith or involving a knowing
   violation of law or (c) resulting in receipt by such person of an improper
   personal benefit.

         The By-Laws of the Registrant provide that a former, present or future
   director, officer or employee of the Registrant or the legal representative
   of any such director, officer or employee shall be indemnified by the
   Registrant:

                  (a) against reasonable costs, disbursements and counsel fees
         paid or incurred where such person has been successful in the defense
         on the merits or otherwise of any pending, threatened or completed
         civil, criminal, administrative or arbitrative action, suit or
         proceeding, and any appeal therein and any inquiry or investigation
         which could lead to such action, suit, or proceeding or in defense of
         any claim, issue or matter therein, brought by reason of such person's
         being or having been such director, officer or employee, and

                  (b) with respect to the defense of any such action, suit,
         proceeding, inquiry or investigation for which indemnification is not
         made under (a) above, against reasonable costs, disbursements (which
         shall include amounts paid in satisfaction of settlements, judgments,
         fines and penalties, exclusive, however, of any amount paid or payable
         to the Registrant) and counsel

                                       3

<PAGE>   4

         fees if such person acted in good faith and in a manner such person
         reasonably believed to be in or not opposed to the best interests of
         the Registrant, and in connection with any criminal proceedings such
         person also had no reasonable cause to believe the conduct was
         unlawful, with the determination as to whether the applicable standard
         of conduct was met to be made by a majority of the members of the
         Board of Directors (sitting as a Committee of the Board) who were not
         parties to such inquiry, investigation, action, suit or proceeding or
         by any one or more disinterested counsel to whom the question may be
         referred by the Board of Directors; provided, however, in connection
         with any proceeding by or in the right of the Registrant, no
         indemnification shall be provided as to any person adjudged by any
         court to be liable to the Registrant except as and to the extent
         determined by such court.

         The Registrant enters into indemnification agreements with its
   directors and officers and enters into insurance agreements on its own
   behalf. The indemnification agreements provide that the Registrant agrees to
   hold harmless and indemnify its directors and officers to the fullest extent
   authorized or permitted by the Business Corporation Act of the State of New
   Jersey, or any other applicable law, or by any amendment thereof or other
   statutory provisions authorizing or permitting such indemnification that is
   adopted after the date hereof. Without limiting the generality of the
   foregoing, the Registrant agrees to hold harmless and indemnify its
   directors and officers to the fullest extent permitted by applicable law
   against any and all expenses, judgments, fines, and amounts paid in
   settlement actually and reasonably incurred by its directors and officers in
   connection with the defense of any present or future threatened, pending, or
   completed claim, action, suit, or proceeding by reason of the fact that they
   were, are, shall be, or shall have been a director or officer of the
   Registrant, or are or were serving, shall serve, or shall have served, at
   the request of the Registrant, as director or officer of another
   corporation, partnership, joint venture, trust, employee benefit plan, or
   other enterprise.

   ITEM 7.           EXEMPTION FROM REGISTRATION CLAIMED

                     Not applicable.

   ITEM 8.           EXHIBITS

                    3(a)      Restated Certificate of Incorporation of the
                              Registrant (May 6, 1992) (Incorporated by
                              reference to Form 10-K Annual Report for the
                              fiscal year ended December 31, 1992)

                    3(b)      Certificate of Amendment to the Certificate of
                              Incorporation of Merck & Co., Inc. (as amended
                              January 14, 1999, effective February 16, 1999)
                              (Incorporated by reference to Form 10-K Annual
                              Report for the fiscal year ended December 31,
                              1998)

                    3(c)      By-laws of the Registrant (as amended effective
                              February 25, 1997) (Incorporated by reference to
                              Form 10-Q Quarterly Report for the period ended
                              March 31, 1997)

                    5         Opinion of Consent of Celia A. Colbert, Vice
                              President, Secretary & Assistant General Counsel
                              of the Registrant

                    23        Consent of Arthur Andersen LLP

                                       4

<PAGE>   5

                    24        Certified Resolution of Board of Directors and
                              Power of Attorney

                    99        Merial 401(k) Savings Plan

   ITEM 9.           UNDERTAKINGS

            1.       The undersigned Registrant hereby undertakes:

                    (a)       To file, during any period in which offers or
                     sales are being made, a post-effective amendment to this
                     Registration Statement to include any material information
                     with respect to the plan of distribution not previously
                     disclosed in the Registration Statement or any material
                     change to such information in the Registration Statement.

                     (b)      That, for the purpose of determining any
                     liability under the Securities Act, each such
                     post-effective amendment shall be deemed to be a new
                     registration statement relating to the securities offered
                     therein, and the offering of such securities at that time
                     shall be deemed to be the initial bona fide offering
                     thereof.

                     (c)      To remove from registration by means of a
                     post-effective amendment any of the securities being
                     registered which remain unsold at the termination of the
                     offering.

            2.       That, for the purpose of determining any liability under
                     the Securities Act, each filing of the Registrant's annual
                     report pursuant to Section 13(a) or 15(d) of the Exchange
                     Act (and, where applicable, each filing of an employee
                     benefit plan's annual report pursuant to Section 15(d) of
                     the Exchange Act) that is incorporated by reference in
                     this Registration Statement shall be deemed to be a new
                     registration statement relating to the securities offered
                     therein, and the offering of such securities at that time
                     shall be deemed to be the initial bona fide offering
                     thereof.

            3.       Insofar as indemnification for liabilities arising under
                     the Securities Act may be permitted to directors, officers
                     and controlling persons of the Registrant pursuant to the
                     foregoing provisions, or otherwise, the Registrant has
                     been advised that in the opinion of the Commission such
                     indemnification is against public policy as expressed in
                     the Act and is, therefore, unenforceable.  In the event
                     that a claim for indemnification against such liabilities
                     (other than the payment by the Registrant of expenses
                     incurred or paid by a director, officer or controlling
                     person of the Registrant in the successful defense of any
                     action, suit or proceeding) is asserted by such director,
                     officer or controlling person in connection with the
                     securities being registered, the Registrant will, unless
                     in the opinion of its counsel the matter has been settled
                     by controlling precedent, submit to a court of appropriate
                     jurisdiction the question whether such indemnification by
                     it is against public policy as expressed in the Act and
                     will be governed by the final adjudication of such issue.

                                       5

<PAGE>   6

                                   SIGNATURES

            Pursuant to the requirements of the Securities Act of 1933, the
   Registrant certifies that it has reasonable grounds to believe that it meets
   all the requirements for filing on Form S-8 and has duly caused this
   Registration Statement to be signed on its behalf by the undersigned,
   thereunto duly authorized, in the City of Whitehouse Station and the State
   of New Jersey, on this 6th day of March, 2000.

                                             MERCK & CO., INC.
                                                (REGISTRANT)

                                   By:      /s/ Celia A. Colbert
                                            ----------------------
                                            Celia A. Colbert
                                            Vice President, Secretary and
                                            Assistant General Counsel

            Pursuant to the requirements of the Securities Act, this
   Registration Statement has been signed by the following persons in the
   capacities and on the dates indicated.

<TABLE>
<CAPTION>
            SIGNATURE                           TITLE                                     DATE
            ---------                           -----                                     ----
<S>                                    <C>                                      <C>
                *                                                                  March 6, 2000
------------------------------
   Raymond V. Gilmartin                Chairman of the Board,
                                       President and Chief Executive
                                       Officer
                                       (principal executive officer)

                *                                                                  March 6, 2000
------------------------------
   Judy C. Lewent                      Senior Vice President and
                                       Chief Financial Officer
                                       (principal financial officer)

                *                                                                  March 6, 2000
------------------------------
   Richard C. Henriques, Jr.           Vice President, Controller
                                       (principal accounting officer)

                *                                                                  March 6, 2000
------------------------------
   H. Brewster Atwater, Jr.            Director

                *                                                                  March 6, 2000
------------------------------
   Derek Birkin                        Director

                *                                                                  March 6, 2000
------------------------------
   Lawrence A. Bossidy                 Director
</TABLE>


   *    Celia A. Colbert, by signing her name hereto, does hereby sign this
        document pursuant to powers of attorney duly executed by the persons
        named, filed with the Securities and Exchange Commission as an exhibit
        to this document, on behalf of such persons, all in the capacities and
        on the date stated, such persons including a majority of the directors
        of the Company.

                                       6

<PAGE>   7

<TABLE>
<S>                                   <C>                                       <C>
               *                                                                 March 6, 2000
------------------------------
   William G. Bowen                    Director

                *                                                                March 6, 2000
------------------------------
   Johnnetta B. Cole                   Director

                *                                                                March 6, 2000
------------------------------
   Carolyne K. Davis                   Director

                *                                                                March 6, 2000
------------------------------
   Lloyd C. Elam                       Director

                                                                                 March 6, 2000
------------------------------
   Charles E. Exley, Jr.               Director

                *                                                                March 6, 2000
------------------------------
   Carleton S. Fiorina                 Director

                *                                                                March 6, 2000
------------------------------
   William B. Harrison, Jr.            Director

               *                                                                 March 6, 2000
------------------------------
   William N. Kelley                   Director

                *                                                                March 6, 2000
------------------------------
   Edward M. Scolnick                  Director

                *                                                                March 6, 2000
------------------------------
   Samuel O. Thier                     Director

                *                                                                March 6, 2000
------------------------------
   Dennis Weatherstone                 Director
</TABLE>


   *    Celia A. Colbert, by signing her name hereto, does hereby sign this
        document pursuant to powers of attorney duly executed by the persons
        named, filed with the Securities and Exchange Commission as an exhibit
        to this document, on behalf of such persons, all in the capacities and
        on the date stated, such persons including a majority of the directors
        of the Company.

                                     By:      /s/ Celia A. Colbert
                                              ----------------------------------
                                              Celia A. Colbert
                                              Vice President, Secretary and
                                              Assistant General Counsel
                                              Attorney-in-Fact


                                       7
<PAGE>   8


         Pursuant to the requirements of the Securities Act, the administrative
committee of the Plan has duly caused this Registration Statement to be signed
on its behalf by the undersigned, thereunto duly authorized, in Iselin, New
Jersey, on this 6th day of March, 2000.

                                                 MERIAL 401(k) SAVINGS PLAN
                                                            (PLAN)

                                        By:        /s/ Robert Stewart
                                                 -------------------------------
                                                 Robert Stewart
                                                 Executive Director, Human
                                                 Resources, North America


                                                   /s/ Philip Forte
                                                 ------------------------------
                                                 Philip Forte
                                                 Executive Director, Finance


                                      8
<PAGE>   9

                               INDEX TO EXHIBITS

<TABLE>
<CAPTION>
   EXHIBIT NO.                                   DESCRIPTION
<S>                          <C>
       3(a)                   Restated Certificate of Incorporation of the
                              Registrant (May 6, 1992) (Incorporated by
                              reference to Form 10-K Annual Report for the
                              fiscal year ended December 31, 1992)

       3(b)                   Certificate of Amendment to the Certificate of
                              Incorporation of Merck & Co., Inc. (as amended
                              January 14, 1999, effective February 16, 1999)
                              (Incorporated by reference to Form 10-K Annual
                              Report for the fiscal year ended December 31,
                              1998)

       3(c)                   By-laws of the Registrant (as amended effective
                              February 25, 1997) (Incorporated by reference to
                              Form 10-Q Quarterly Report for the period ended
                              March 31, 1997)

       5                      Opinion of Consent of Celia A. Colbert, Vice
                              President, Secretary and Assistant General
                              Counsel of the Registrant

       23                     Consent of Arthur Andersen LLP

       24                     Certified Resolution of Board of Directors and
                              Power of Attorney

       99                     Merial 401(k) Savings Plan
</TABLE>

                                       9
[{"type": "S-8", "sequence": "1", "description": "MERCK & CO., INC.", "secsgml_size_bytes": 28584}]
{"company-data": {"conformed-name": "MERCK & CO INC", "cik": "0000064978", "assigned-sic": "2834", "irs-number": "221109110", "state-of-incorporation": "NJ", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-31762", "film-number": "561359"}, "business-address": {"street1": "ONE MERCK DR", "street2": "P O BOX 100", "city": "WHITEHOUSE STATION", "state": "NJ", "zip": "08889-0100", "phone": "9084234044"}, "mail-address": {"street1": "ONE MERCK DR", "street2": "PO BOX 100 WS3AB-05", "city": "WHITEHOUSE STATION", "state": "NJ", "zip": "08889-0100"}}
1

AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON MARCH 6, 2000
                                                       REGISTRATION NO. 333-____

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

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                             ----------------------

                                    FORM S-8

            REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933

                               MERCK & CO., INC.
             (Exact Name of Registrant as Specified in its Charter)
NEW JERSEY                                                            22-1109110
(State or Other Jurisdiction of Incorporation or Organization)                   (I.R.S. Employer Identification No.)
P.O. BOX 100
                                ONE MERCK DRIVE
                       WHITEHOUSE STATION, NJ 08889-0100
         (Address, Including Zip Code, of Principal Executive Offices)

                           MERIAL 401(k) SAVINGS PLAN
                            (Full Title of the Plan)

                                CELIA A. COLBERT
            VICE PRESIDENT, SECRETARY AND ASSISTANT GENERAL COUNSEL
                               MERCK & CO., INC.
                                  P.O. BOX 100
                   WHITEHOUSE STATION, NEW JERSEY 08889-0100
                                 (908) 423-1000
           (Name, Address, Including Zip Code, and Telephone Number,
                   Including Area Code, of Agent for Service)

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

                                With a copy to:
                             WARREN J. CASEY, ESQ.
                        PITNEY, HARDIN, KIPP & SZUCH LLP
                                 P.O. BOX 1945
                       MORRISTOWN, NEW JERSEY 07962-1945
                                 (973) 966-6300

                        CALCULATION OF REGISTRATION FEE
Title of                  Amount             Proposed Maximum        Proposed Maximum            Amount Of
     Securities To                To Be               Offering Price             Aggregate              Registration
     Be Registered              Registered              Per Share             Offering Price                Fee
------------------------- ----------------------- ----------------------- ------------------------ -----------------------
Common Stock (Par Value
$.01 per share)               200,000 (1)                $60.75 (2)          $12,150,000 (2)              $3,207.60

Plan interests related       An indeterminate              N/A                      N/A                     N/A
to Merial Limited             amount of plan
401(k) Savings                interests (3)
Plan............
------------------------- ----------------------- ----------------------- ------------------------ -----------------------
(1)  Based on an estimate of the number of shares that will be purchased
         pursuant to the Merial Limited 401(k) Savings Plan. Pursuant to Rule
         416(c) of the Securities Act of 1933, as amended (the "Securities
         Act"), there is also being registered such number of additional shares
         that may become available for purchase pursuant to such plan in the
         event of certain changes in the outstanding shares, including
         reorganizations, mergers, recapitalizations, restructurings, stock
         dividends, stock splits, reverse stock splits and reclassifications.

    (2)  Estimated pursuant to paragraphs (c) and (h) of Rule 457 of the
         Securities Act, solely for the purpose of calculating the registration
         fee, based upon the average of the high and low sales prices of shares
         of Common Stock on March 1, 2000, as reported on the New York
         Stock Exchange.

    (3)  Pursuant to Rule 416 (c) of the Securities Act, this Registration
         Statement covers an indeterminate amount of plan interests to be
         offered or sold pursuant to the Merial Limited 401(k) Savings Plan
         attached as an exhibit hereto.
2

                                     PART I

              INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

            The document(s) containing the information specified in this Part I
   will be sent or given to employees as specified by Rule 428(b)(1)
   promulgated under the Securities Act. Such documents need not be filed with
   the Securities and Exchange Commission (the "Commission").

                                    PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

   ITEM 3.           INCORPORATION OF DOCUMENTS BY REFERENCE

            The following documents filed by Merck & Co., Inc. (the
   "Registrant") (Exchange Act File No. 1-3305) with the Commission are
   incorporated herein and made a part hereof:

            (a)      Annual Report on Form 10-K, filed on March 24, 1999, for
                     the fiscal year ended December 31, 1998;

            (b)      Proxy Statement for the Annual Meeting of Stockholders
                     held on April 27, 1999, filed on March 18, 1999;

            (c)      Quarterly Report on Form 10-Q, filed on May 12, 1999, for
                     the quarter ended March 31, 1999;

            (d)      Form 10-K/A, filed on June 11, 1999, amending the
                     Registrant's Annual Report on Form 10-K for the fiscal
                     year ended December 31, 1998;

            (e)      Quarterly Report on Form 10-Q, filed on August 12, 1999,
                     for the quarter ended June 30, 1999;

            (f)      Quarterly Report on Form 10-Q, filed on November 12, 1999,
                     for the quarter ended September 30, 1999;

            (g)      Current Report on Form 8-K dated December 9, 1999, filed
                     on December 16, 1999; and

            (h)      The descriptions of the Common Stock of the Registrant set
                     forth in the Registrant's Registration Statements pursuant
                     to Section 12 of the Exchange Act, and any amendment or
                     report filed for the purpose of updating such description.

            All reports or other documents filed by the Registrant pursuant to
   Sections 13, 14 or 15(d) of the Securities Exchange Act of 1934, as amended
   (the "Exchange Act") and prior to the filing of a post-effective amendment
   which indicates that all securities offered have been sold or which
   deregisters all securities then remaining unsold, hereby are incorporated
   herein by reference and shall be deemed a part hereof from the date of
   filing of such documents. An Exhibit Index can be found on page 9 of this
   Registration Statement. 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 of this Registration Statement to the
   extent that a statement contained herein or in any other subsequently filed
   document which 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 Registration Statement.

                                       2
3

   ITEM 4.           DESCRIPTION OF SECURITIES

                     Not applicable.

   ITEM 5.           INTERESTS OF NAMED EXPERTS AND COUNSEL

           The validity of the Common Stock will be passed upon for the
   Registrant by Celia A. Colbert, Vice President, Secretary & Assistant
   General Counsel of the Company.

   ITEM 6.           INDEMNIFICATION OF DIRECTORS AND OFFICERS

         The New Jersey Business Corporation Act provides that a New Jersey
   corporation has the power to indemnify a director or officer against his or
   her expenses and liabilities in connection with any proceeding involving the
   director or officer by reason of his or her being or having been such a
   director or officer, other than a proceeding by or in the right of the
   corporation, if such a director or officer acted in good faith and in a
   manner he or she reasonably believed to be in or not opposed to the best
   interests of the corporation; and with respect to any criminal proceeding,
   such director or officer had no reasonable cause to believe his or her
   conduct was unlawful.

         The indemnification and advancement of expenses shall not exclude any
   other rights, including the right to be indemnified against liabilities and
   expenses incurred in proceedings by or in the right of the corporation, to
   which a director or officer may be entitled under a certificate of
   incorporation, bylaw, agreement, vote of shareholders, or otherwise;
   provided that no indemnification shall be made to or on behalf of a director
   or officer if a judgment or other final adjudication adverse to the director
   or officer establishes that his or her acts or omissions (a) were in breach
   of his or her duty of loyalty to the corporation or its shareholders, (b)
   were not in good faith or involved a knowing violation of law or (c)
   resulted in receipt by the director or officer of an improper personal
   benefit.

         The Registrant's Restated Certificate of Incorporation provides that,
   to the fullest extent permitted by the laws of the State of New Jersey,
   directors and officers of the Registrant shall not be personally liable to
   the Registrant or its stockholders for damages for breach of any duty owed
   to the Registrant or its stockholders, except that a director or officer
   shall not be relieved from liability for any breach of duty based upon an
   act or omission (a) in breach of such person's duty of loyalty to the
   Registrant or its stockholders, (b) not in good faith or involving a knowing
   violation of law or (c) resulting in receipt by such person of an improper
   personal benefit.

         The By-Laws of the Registrant provide that a former, present or future
   director, officer or employee of the Registrant or the legal representative
   of any such director, officer or employee shall be indemnified by the
   Registrant:

                  (a) against reasonable costs, disbursements and counsel fees
         paid or incurred where such person has been successful in the defense
         on the merits or otherwise of any pending, threatened or completed
         civil, criminal, administrative or arbitrative action, suit or
         proceeding, and any appeal therein and any inquiry or investigation
         which could lead to such action, suit, or proceeding or in defense of
         any claim, issue or matter therein, brought by reason of such person's
         being or having been such director, officer or employee, and

                  (b) with respect to the defense of any such action, suit,
         proceeding, inquiry or investigation for which indemnification is not
         made under (a) above, against reasonable costs, disbursements (which
         shall include amounts paid in satisfaction of settlements, judgments,
         fines and penalties, exclusive, however, of any amount paid or payable
         to the Registrant) and counsel

                                       3
4

         fees if such person acted in good faith and in a manner such person
         reasonably believed to be in or not opposed to the best interests of
         the Registrant, and in connection with any criminal proceedings such
         person also had no reasonable cause to believe the conduct was
         unlawful, with the determination as to whether the applicable standard
         of conduct was met to be made by a majority of the members of the
         Board of Directors (sitting as a Committee of the Board) who were not
         parties to such inquiry, investigation, action, suit or proceeding or
         by any one or more disinterested counsel to whom the question may be
         referred by the Board of Directors; provided, however, in connection
         with any proceeding by or in the right of the Registrant, no
         indemnification shall be provided as to any person adjudged by any
         court to be liable to the Registrant except as and to the extent
         determined by such court.

         The Registrant enters into indemnification agreements with its
   directors and officers and enters into insurance agreements on its own
   behalf. The indemnification agreements provide that the Registrant agrees to
   hold harmless and indemnify its directors and officers to the fullest extent
   authorized or permitted by the Business Corporation Act of the State of New
   Jersey, or any other applicable law, or by any amendment thereof or other
   statutory provisions authorizing or permitting such indemnification that is
   adopted after the date hereof. Without limiting the generality of the
   foregoing, the Registrant agrees to hold harmless and indemnify its
   directors and officers to the fullest extent permitted by applicable law
   against any and all expenses, judgments, fines, and amounts paid in
   settlement actually and reasonably incurred by its directors and officers in
   connection with the defense of any present or future threatened, pending, or
   completed claim, action, suit, or proceeding by reason of the fact that they
   were, are, shall be, or shall have been a director or officer of the
   Registrant, or are or were serving, shall serve, or shall have served, at
   the request of the Registrant, as director or officer of another
   corporation, partnership, joint venture, trust, employee benefit plan, or
   other enterprise.

   ITEM 7.           EXEMPTION FROM REGISTRATION CLAIMED

                     Not applicable.

   ITEM 8.           EXHIBITS

                    3(a)      Restated Certificate of Incorporation of the
                              Registrant (May 6, 1992) (Incorporated by
                              reference to Form 10-K Annual Report for the
                              fiscal year ended December 31, 1992)

                    3(b)      Certificate of Amendment to the Certificate of
                              Incorporation of Merck & Co., Inc. (as amended
                              January 14, 1999, effective February 16, 1999)
                              (Incorporated by reference to Form 10-K Annual
                              Report for the fiscal year ended December 31,
                              1998)

                    3(c)      By-laws of the Registrant (as amended effective
                              February 25, 1997) (Incorporated by reference to
                              Form 10-Q Quarterly Report for the period ended
                              March 31, 1997)

                    5         Opinion of Consent of Celia A. Colbert, Vice
                              President, Secretary & Assistant General Counsel
                              of the Registrant

                    23        Consent of Arthur Andersen LLP

                                       4
5

                    24        Certified Resolution of Board of Directors and
                              Power of Attorney

                    99        Merial 401(k) Savings Plan

   ITEM 9.           UNDERTAKINGS

            1.       The undersigned Registrant hereby undertakes:

                    (a)       To file, during any period in which offers or
                     sales are being made, a post-effective amendment to this
                     Registration Statement to include any material information
                     with respect to the plan of distribution not previously
                     disclosed in the Registration Statement or any material
                     change to such information in the Registration Statement.

                     (b)      That, for the purpose of determining any
                     liability under the Securities Act, each such
                     post-effective amendment shall be deemed to be a new
                     registration statement relating to the securities offered
                     therein, and the offering of such securities at that time
                     shall be deemed to be the initial bona fide offering
                     thereof.

                     (c)      To remove from registration by means of a
                     post-effective amendment any of the securities being
                     registered which remain unsold at the termination of the
                     offering.

            2.       That, for the purpose of determining any liability under
                     the Securities Act, each filing of the Registrant's annual
                     report pursuant to Section 13(a) or 15(d) of the Exchange
                     Act (and, where applicable, each filing of an employee
                     benefit plan's annual report pursuant to Section 15(d) of
                     the Exchange Act) that is incorporated by reference in
                     this Registration Statement shall be deemed to be a new
                     registration statement relating to the securities offered
                     therein, and the offering of such securities at that time
                     shall be deemed to be the initial bona fide offering
                     thereof.

            3.       Insofar as indemnification for liabilities arising under
                     the Securities Act may be permitted to directors, officers
                     and controlling persons of the Registrant pursuant to the
                     foregoing provisions, or otherwise, the Registrant has
                     been advised that in the opinion of the Commission such
                     indemnification is against public policy as expressed in
                     the Act and is, therefore, unenforceable.  In the event
                     that a claim for indemnification against such liabilities
                     (other than the payment by the Registrant of expenses
                     incurred or paid by a director, officer or controlling
                     person of the Registrant in the successful defense of any
                     action, suit or proceeding) is asserted by such director,
                     officer or controlling person in connection with the
                     securities being registered, the Registrant will, unless
                     in the opinion of its counsel the matter has been settled
                     by controlling precedent, submit to a court of appropriate
                     jurisdiction the question whether such indemnification by
                     it is against public policy as expressed in the Act and
                     will be governed by the final adjudication of such issue.

                                       5
6

                                   SIGNATURES

            Pursuant to the requirements of the Securities Act of 1933, the
   Registrant certifies that it has reasonable grounds to believe that it meets
   all the requirements for filing on Form S-8 and has duly caused this
   Registration Statement to be signed on its behalf by the undersigned,
   thereunto duly authorized, in the City of Whitehouse Station and the State
   of New Jersey, on this 6th day of March, 2000.

                                             MERCK & CO., INC.
                                                (REGISTRANT)

                                   By:      /s/ Celia A. Colbert
                                            ----------------------
                                            Celia A. Colbert
                                            Vice President, Secretary and
                                            Assistant General Counsel

            Pursuant to the requirements of the Securities Act, this
   Registration Statement has been signed by the following persons in the
   capacities and on the dates indicated.
SIGNATURE                           TITLE                                     DATE
            ---------                           -----                                     ----
*                                                                  March 6, 2000
------------------------------
   Raymond V. Gilmartin                Chairman of the Board,
                                       President and Chief Executive
                                       Officer
                                       (principal executive officer)

                *                                                                  March 6, 2000
------------------------------
   Judy C. Lewent                      Senior Vice President and
                                       Chief Financial Officer
                                       (principal financial officer)

                *                                                                  March 6, 2000
------------------------------
   Richard C. Henriques, Jr.           Vice President, Controller
                                       (principal accounting officer)

                *                                                                  March 6, 2000
------------------------------
   H. Brewster Atwater, Jr.            Director

                *                                                                  March 6, 2000
------------------------------
   Derek Birkin                        Director

                *                                                                  March 6, 2000
------------------------------
   Lawrence A. Bossidy                 Director
*    Celia A. Colbert, by signing her name hereto, does hereby sign this
        document pursuant to powers of attorney duly executed by the persons
        named, filed with the Securities and Exchange Commission as an exhibit
        to this document, on behalf of such persons, all in the capacities and
        on the date stated, such persons including a majority of the directors
        of the Company.

                                       6
7
*                                                                 March 6, 2000
------------------------------
   William G. Bowen                    Director

                *                                                                March 6, 2000
------------------------------
   Johnnetta B. Cole                   Director

                *                                                                March 6, 2000
------------------------------
   Carolyne K. Davis                   Director

                *                                                                March 6, 2000
------------------------------
   Lloyd C. Elam                       Director

                                                                                 March 6, 2000
------------------------------
   Charles E. Exley, Jr.               Director

                *                                                                March 6, 2000
------------------------------
   Carleton S. Fiorina                 Director

                *                                                                March 6, 2000
------------------------------
   William B. Harrison, Jr.            Director

               *                                                                 March 6, 2000
------------------------------
   William N. Kelley                   Director

                *                                                                March 6, 2000
------------------------------
   Edward M. Scolnick                  Director

                *                                                                March 6, 2000
------------------------------
   Samuel O. Thier                     Director

                *                                                                March 6, 2000
------------------------------
   Dennis Weatherstone                 Director
*    Celia A. Colbert, by signing her name hereto, does hereby sign this
        document pursuant to powers of attorney duly executed by the persons
        named, filed with the Securities and Exchange Commission as an exhibit
        to this document, on behalf of such persons, all in the capacities and
        on the date stated, such persons including a majority of the directors
        of the Company.

                                     By:      /s/ Celia A. Colbert
                                              ----------------------------------
                                              Celia A. Colbert
                                              Vice President, Secretary and
                                              Assistant General Counsel
                                              Attorney-in-Fact

                                       7
8

         Pursuant to the requirements of the Securities Act, the administrative
committee of the Plan has duly caused this Registration Statement to be signed
on its behalf by the undersigned, thereunto duly authorized, in Iselin, New
Jersey, on this 6th day of March, 2000.

                                                 MERIAL 401(k) SAVINGS PLAN
                                                            (PLAN)

                                        By:        /s/ Robert Stewart
                                                 -------------------------------
                                                 Robert Stewart
                                                 Executive Director, Human
                                                 Resources, North America

                                                   /s/ Philip Forte
                                                 ------------------------------
                                                 Philip Forte
                                                 Executive Director, Finance

                                      8
9

                               INDEX TO EXHIBITS
EXHIBIT NO.                                   DESCRIPTION
3(a)                   Restated Certificate of Incorporation of the
                              Registrant (May 6, 1992) (Incorporated by
                              reference to Form 10-K Annual Report for the
                              fiscal year ended December 31, 1992)

       3(b)                   Certificate of Amendment to the Certificate of
                              Incorporation of Merck & Co., Inc. (as amended
                              January 14, 1999, effective February 16, 1999)
                              (Incorporated by reference to Form 10-K Annual
                              Report for the fiscal year ended December 31,
                              1998)

       3(c)                   By-laws of the Registrant (as amended effective
                              February 25, 1997) (Incorporated by reference to
                              Form 10-Q Quarterly Report for the period ended
                              March 31, 1997)

       5                      Opinion of Consent of Celia A. Colbert, Vice
                              President, Secretary and Assistant General
                              Counsel of the Registrant

       23                     Consent of Arthur Andersen LLP

       24                     Certified Resolution of Board of Directors and
                              Power of Attorney

       99                     Merial 401(k) Savings Plan
9