EXHIBIT 5


                        [LETTERHEAD OF MARGARET M. FORAN]


April 16, 2003


Pfizer Inc.
235 East 42nd Street
New York, New York 10017-5755

Pfizer Inc.:

      In connection with the Registration Statement on Form S-8 relating to a
total of 61,313,102 shares of Common Stock of Pfizer Inc. under the Pharmacia
Corporation Management Incentive Plan, the Pharmacia Corporation 1996 Long-Term
Incentive Plan, and the Pharmacia Corporation 2001 Long-Term Incentive Plan,
(collectively, the "Plans") adopted and assumed by Pfizer Inc. in connection
with the merger with the Pharmacia Corporation, it is my opinion that:

      All necessary corporate proceedings have been taken to authorize the
issuance of the shares under the Plans, and all such shares, upon issuance in
accordance with the Plans and upon full payment in cash for such shares issued,
will be validly issued and outstanding and fully paid and non-assessable.

      In preparing this opinion, I have examined certificates of public
officials, certificates of officers and copies certified to my satisfaction of
such corporate documents and records of the Company and such other papers as I
have thought relevant and necessary as a basis for my opinion. I have relied on
such certificates in connection with the accuracy of actual matters contained in
such documents which were not independently established.

      I consent to the use of this opinion in the Registration Statement and to
the reference to my name under the heading "Legal Opinion" in the Prospectus. In
giving such consent, I do not admit that I come within 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.

                                          Very truly yours,


                                          /s/ MARGARET M. FORAN
                                          ---------------------------
                                          MARGARET M. FORAN

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