EXHIBIT 5

                               April 26, 2002

Board of Directors
Merck & Co., Inc.
One Merck Drive
Whitehouse Station, NJ  08889-0100

Re:    Merck & Co., Inc. - Common Stock

Ladies and Gentlemen:

         I am the Vice President, Secretary & Assistant General Counsel of
Merck & Co., Inc., a New Jersey corporation (the "Corporation"), and in such
capacity have acted as counsel for the Company in connection with the proposed
registration under the Securities Act of 1933, as amended, of up to 6,000,000
shares of the common stock, Par Value $0.01 per share (the "Shares"), of the
Corporation, which may be issued by the Corporation pursuant to the Merck Stock
Investment Plan or any successor plans thereto, as such plans or successor plans
may be amended from time to time. I have examined such corporate records and
other documents, including the Registration Statement on Form S-3 relating to
the Shares, and have reviewed such matters of law as I have deemed necessary for
this opinion.

         I am admitted to the Bar of the State of New York. The opinions
expressed herein are limited in all respects to the federal laws of the United
States of America, the laws of the State of New York, and the Business
Corporation Act of the State of New Jersey.

         On the basis of the foregoing examination and review, I advise you
that, in my opinion:

         1.       The Corporation is a corporation duly
                  organized and existing under the laws of
                  the State of New Jersey.

         2.       All necessary corporate action on the part of the Corporation
                  has been taken to authorize the issuance of the Shares, and,
                  when issued as described in the Registration Statement, the
                  Shares will be legally and validly issued, fully paid, and
                  nonassessable.

         The opinions expressed herein are rendered only to you and are solely
for your benefit and may not be relied upon by any person, firm, or corporation
for any reason without my prior written consent.

         I consent to the filing of this opinion as an exhibit to the
Registration Statement. In giving this consent, I do not admit that I am in the
category of persons whose consent is required under Section 7 of the Securities
Act of 1933 or the rules and regulations of the Securities and Exchange
Commission thereunder.

                               Very truly yours,

                               /s/ Celia A. Colbert