As filed with the Securities and Exchange Commission on July 29, 2004

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION

FORM S-8

MERCK & CO., INC.

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

CELIA A. COLBERT
Vice President, Secretary & Assistant General Counsel
MERCK & CO., INC.
P.O. Box 100
Whitehouse Station, New Jersey 08889-0100
(908) 423-1000
(Name, Address and Telephone Number of Agent for Service)

If any of the securities being registered on this Form are to be offered on a delayed or
continuous basis pursuant to Rule 415 under the Securities Act of 1933, other than securities
offered only in connection with dividend or interest reinvestment plans, check the following box. x

CALCULATION OF REGISTRATION FEE

Table of Contents

PART II

INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3. Incorporation of Documents by Reference

     The following documents filed by the registrant (Exchange Act File No. 1-3305) with the Securities and Exchange Commission are incorporated herein by reference and made a part hereof:

     All documents filed by the registrant pursuant to Section 13, 14 or 15(d) of the Exchange Act from the date hereof and prior to the termination of the offering of the securities offered hereby shall be deemed to be incorporated by reference herein and to be a part hereof from the date of filing of such documents. An Exhibit Index can be found on page 12 of this Registration Statement.

Item 4. Description of Securities

     Not applicable.

Item 5. Interests of Named Experts and Counsel

     The validity of the Common Stock and interests in the plan will be passed upon for the Company 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

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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 stockholders, 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 stockholders, (b) were not in good faith or involved in a knowing violation of law or (c) resulted in receipt by the director or officer of an improper personal benefit.

     The Company’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 Company shall not be personally liable to the Company or its stockholders for damages for breach of any duty owed to the Company 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 Company 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 Company provide that a former, present or future director, officer or employee of the Company or the legal representative of any such director, officer or employee shall be indemnified by the Company:

     (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

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penalties, exclusive, however, of any amount paid or payable to the Company) and counsel 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 Company, 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 Company, no indemnification shall be provided as to any person adjudged by any court to be liable to the Company except as and to the extent determined by such court.

     The Company enters into indemnification agreements with its directors and officers and enters into insurance agreements on its own behalf. The indemnification agreements provide that the Company 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 Company 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 Company, or are or were serving, shall serve or shall have served, at the request of the Company, 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.

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Item 8. Exhibits

Item 9. Undertakings

     The undersigned registrant hereby undertakes:

1. (a) To file, during any period in which offers or sales are being made, a post-effective amendment to the 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.

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     (b) That, for the purpose of determining any liability under the Securities Act of 1933, 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.

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SIGNATURES

     Pursuant to the requirements of the Securities Act of 1933, the issuer 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 Town of Whitehouse Station and the State of New Jersey on the 29^th day of July 2004.

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

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     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 Duluth, Georgia, on this 29^th day of July, 2004.

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EXHIBIT 23

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

     We hereby consent to the incorporation by reference in this Registration Statement on Form S-8 of our report dated February 20, 2004 relating to the consolidated financial statements of Merck & Co., Inc. and its subsidiaries, which appears in the 2003 Annual Report to Stockholders, which is incorporated by reference in Merck & Co., Inc.’s Annual Report on Form 10-K for the year ended December 31, 2003.

/s/PricewaterhouseCoopers LLP

Florham Park, New Jersey
July 27, 2004

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EXHIBIT INDEX

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