EXHIBIT 5



                               October 31, 2001

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

Ladies and Gentlemen:

In connection with the registration under the Securities Act of 1933, as amended
(the "Act"), of $1,500,000,000 aggregate principal amount of debt securities
(the "Securities") of Merck & Co., Inc., a New Jersey corporation (the
"Company"), I, as Senior Vice President and General Counsel of the Company, or
attorneys under my general supervision, have examined such corporate records,
certificates and other documents and such questions of law as I have considered
necessary or appropriate for the purposes of this opinion. Upon the basis of
such examination, I advise you that, in my opinion:

1.     The Company has been duly incorporated and is an existing corporation in
       good standing under the laws of the state of New Jersey.

2.     When the Registration Statement has become effective under the Act, the
       terms of the Securities and of their issue and sale have been duly
       established in conformity with the Indenture relating to the Securities
       so as not to violate any applicable law or agreement or instrument then
       binding on the Company, and the Securities have been duly executed and
       authenticated in accordance with such Indenture and issued and sold as
       contemplated in the Registration Statement, the Securities will
       constitute valid and binding obligations of the Company, subject to
       bankruptcy, insolvency, fraudulent transfer, reorganization, moratorium
       and similar laws of general applicability relating to or affecting
       creditors' rights and to general equity principles.

I hereby consent to the filing of this opinion as an exhibit to the Registration
Statement and to the reference to me under the heading "Validity of Debt
Securities" in the Prospectus. In giving such consent, I do not thereby admit
that I am in the category of persons whose consent is required under Section 7
of the Act.

                                Very truly yours,

                                /s/  Kenneth C. Frazier
                                -----------------------
                                     Kenneth C. Frazier