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           As filed with the Securities and Exchange Commission on June 28, 1996
                                                       Registration No. 33-64665

- --------------------------------------------------------------------------------
                       SECURITIES AND EXCHANGE COMMISSION
                              Washington, DC 20549
                                 --------------

                         POST-EFFECTIVE AMENDMENT NO. 2
                                       TO
                                    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             (I.R.S. Employer Identification No.)
 incorporation or organization)

         One Merck Drive
       Whitehouse Station, NJ                            08889-0100
(Address of principal executive offices)                 (Zip Code)

                                ASTRA MERCK INC.
                       EMPLOYEE SAVINGS AND SECURITY PLAN
                            (Full title of the plan)

                                CELIA A. COLBERT
                     Secretary and Assistant General Counsel
                                Merck & Co., Inc.
                                 One Merck Drive
                    Whitehouse Station, New Jersey 08889-0100
                     (Name and address of agent for service)

                                 (908) 423-1000
          (Telephone number, including area code, of agent for service)
                                 --------------

                         Copy of all communications to:

                          ROBERT J. LICHTENSTEIN, ESQ.
                           Morgan, Lewis & Bockius LLP
                              2000 One Logan Square
                             Philadelphia, PA 19103
                                 (215) 963-5726
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                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE.

                  The following documents, as filed by Merck & Co., Inc. (the
"Registrant") with the Securities and Exchange Commission (the "Commission"),
are incorporated by reference in this Registration Statement:

                  (a) Annual Report on Form 10-K, filed on March 20, 1996 for
         the fiscal year ended December 31, 1995;

                  (b) Form 10-K/A filed on June 24, 1996, amending the
         Registrant's Annual Report on Form 10-K for the fiscal year ended
         December 31, 1995;

                  (c) Quarterly Report on Form 10-Q filed on May 14, 1996 for
         the Quarter ended March 31, 1996;

                  (d) Proxy Statement for the Annual Meeting of Stockholders
         held on April 23, 1996;

                  (e) 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.

                  In addition, the Report on Form 11-K for the fiscal year ended
December 31, 1995 with respect to the Astra Merck Inc. Employee Savings and
Security Plan (the "Plan"), filed with the Commission, is incorporated by
reference in this Registration Statement.

                  All reports and other documents filed by the Registrant and
the Plan pursuant to Sections 13(a), 13(c), 14 and 15(d) of the Securities
Exchange Act of 1934, after the date of this registration statement and prior to
the filing of a post-effective amendment that indicates that all securities
offered hereby have been sold or that deregisters all securities then remaining
unsold, shall be deemed to be incorporated by reference herein and to be part
hereof from the date of filing of such documents.

                  Any statement contained in a document 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 is also 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 hereof.

ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.

                  The financial statements incorporated in this Registration
Statement by reference to the Report of the Astra Merck Inc. Employee Savings
and Security Plan on Form 11-K for the fiscal year ended December 31, 1995, have
been so incorporated in reliance on the report of Price Waterhouse LLP,
independent accountants, given on the authority of said firm as experts in
auditing and accounting.

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ITEM 8.  EXHIBITS.

                  The exhibits filed as part of this Registration Statement are
as follows:

Exhibit
Number                         Exhibit
- -------                        -------
  5.1       Opinion re legality (Common Stock of Registrant)*

  5.2       Opinion of Morgan, Lewis & Bockius LLP (interests in Plan)*

 23.1       Consent of Price Waterhouse LLP

 23.2       Consent of Arthur Andersen LLP*

 23.3       Consent of Morgan, Lewis & Bockius LLP (included in Exhibit 5.2)*

 24         Power of Attorney and Certified Resolution of Board of Directors*

 99         Astra Merck Inc. Employee Savings and Security Plan


*  Previously filed

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                                   SIGNATURES

                  The Registrant. Pursuant to the requirements of the Securities
Act of 1933, the Registrant certifies that it has reasonable grounds to believe
that it meets all of the requirements for filing on Form S-8 and has duly caused
this Amendment to be signed on its behalf by the undersigned, thereunto duly
authorized, in Whitehouse Station, New Jersey, on the 25th day of June, 1996.

                                                MERCK & CO., INC.

                                   By:                    *
                                      ------------------------------------------
                                      RAYMOND V. GILMARTIN
                                      Chairman of the Board, President and Chief
                                      Executive Office and Director


                                   By: /s/ Celia A. Colbert
                                      -----------------------------------------
                                      CELIA A. COLBERT
                                      Secretary and Assistant
                                      General Counsel
                                      (Attorney-in-fact)

                  Pursuant to the requirements of the Securities Act 1933, this
Registration Statement has been signed below by the following persons in the
capacities and on the date indicated.

Signatures                 Title                                   Date
- ----------                 -----                                   ----

        *                  Chairman of the Board,                  June 25, 1996
- --------------------       President and Chief Executive Officer;
Raymond V. Gilmartin       Principal Executive Officer; Director

        *                  Senior Vice President                   June 25, 1996
- --------------------       and Chief Accounting Officer; 
Judy C. Lewent             Principal Financial Officer

        *                  Vice President, Controller;             June 25, 1996
- --------------------       Principal Accounting Officer
Peter E. Nugent              

        *                  Director                                June 25, 1996
- --------------------
H. Brewster Atwater, Jr.

        *                  Director                                June 25, 1996
- --------------------
Derek Birkin

        *                  Director                                June 25, 1996
- --------------------
Lawrence A. Bossidy

        *                  Director                                June 25, 1996
- --------------------
William G. Bowen, Ph.D.

                            
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        *                  Director                                June 25, 1996
- --------------------
Johnnetta B. Cole, Ph.D.

        *                  Director                                June 25, 1996
- --------------------
Carolyne K. Davis, Ph.D.

        *                  Director                                June 25, 1996
- --------------------
Lloyd C. Elam, M.D.

        *                  Director                                June 25, 1996
- --------------------
Charles E. Exley, Jr.

        *                  Director                                June 25, 1996
- --------------------
William N. Kelley, M.D.

        *                  Director                                June 25, 1996
- --------------------
Samuel O. Thier, M.D.

        *                  Director                                June 25, 1996
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Dennis Weatherstone

                  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 the
Registration Statement, 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
                                        Secretary and Assistant
                                        General Counsel
                                        (Attorney-in-Fact)

                  The Plan. Pursuant to the requirements of the Securities Act
of 1933, the Plan has duly caused this Amendment to be signed on its behalf by
the undersigned, thereunto duly authorized, in Wayne, Pennsylvania on June 24,
1996.

                                    ASTRA MERCK INC.
                                    EMPLOYEE SAVINGS AND SECURITY PLAN

                                    By: /s/ Linda E. Robertson
                                        --------------------------------  
                                    Name:  Linda E. Robertson
                                    Title:   Administrative Committee