As filed with the Securities and Exchange Commission on
               April 16, 2003 Registration Statement No. 333-98105
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                       SECURITIES AND EXCHANGE COMMISSION
                               450 5TH STREET N.W.
                             WASHINGTON, D.C. 20549

                                   ----------

                     POST-EFFECTIVE AMENDMENT TO FORM S-4 ON
                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933

                                   ----------

                                   PFIZER INC.
             (Exact name of Registrant as specified in its charter)


                DELAWARE                                 13-5315170
--------------------------------------------------------------------------------
          (State of Incorporation)          (I.R.S. Employer Identification No.)


                              235 EAST 42ND STREET
                          NEW YORK, NEW YORK 10017-5755
                    (Address of Principal Executive Offices)

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                 PHARMACIA CORPORATION MANAGEMENT INCENTIVE PLAN
               PHARMACIA CORPORATION 1996 LONG-TERM INCENTIVE PLAN
                 PHARMACIA CORPORATION EQUITY COMPENSATION PLAN
             PHARMACIA CORPORATION SHARED SUCCESS STOCK OPTION PLAN
                      PHARMACIA CORPORATION DIRECTORS' PLAN
               PHARMACIA CORPORATION 2001 LONG-TERM INCENTIVE PLAN
                    SEARLE MONSANTO STOCK OPTION PLAN OF 1986
                       MONSANTO MANAGEMENT PLAN OF 1998/1
                       MONSANTO MANAGEMENT PLAN OF 1988/11
                     NUTRA SWEET/MONSANTO STOCK PLAN OF 1991
                       SEARLE/MONSANTO STOCK PLAN OF 1994
                MONSANTO NON-EMPLOYEE DIRECTOR PLAN OF 9/01/1997
                    THE UPJOHN COMPANY 1992 STOCK OPTION PLAN
                            (Full Title of the Plan)

                             MARGARET M. FORAN, ESQ.
                                   PFIZER INC.
                              235 EAST 42ND STREET
                          NEW YORK, NEW YORK 10017-5755
                     (Name and Address of Agent for Service)

                                 (212) 773-4802
                     (Telephone Number of Agent for Service)

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      This Form S-8 is registering 194,964,673 shares of Pfizer common stock,
$.05 par value, representing the number of shares to be issued upon the exercise
of options or vesting of grants outstanding under each of the following Plans,
after giving effect to the conversion ratio used in connection with the merger
of Pfizer Inc. and Pharmacia Corporation of 1.4 shares of Pfizer Inc. common
stock for each share of Pharmacia Corporation common stock outstanding at the
effective time of the merger: 74,214,342 shares under the Pharmacia Corporation
Management Incentive Plan; 43,788,202 shares under the Pharmacia Corporation
1996 Long-Term Incentive Plan; 15,114,910 shares under the Pharmacia Corporation
Equity Compensation Plan; 12,759,637 shares under the Pharmacia Corporation
Shared Success Stock Option Plan; 135,249 shares under the Pharmacia Corporation
Directors' Plan; 38,779,928 shares under the Pharmacia Corporation 2001
Long-Term Incentive Plan; 205,254 shares under the Searle Monsanto Stock Option
Plan of 1986; 116,011 shares under the Monsanto Management Plan of 1998/1;
1,607,322 shares under the Monsanto Management Plan of 1988/11; 6,473 shares
under the Nutra Sweet/Monsanto Stock Plan of 1991; 7,377,411 shares under the
Searle/Monsanto Stock Plan of 1994; 174,060 shares under the Monsanto
Non-Employee Director Plan of 9/01/1997; and 685,874 shares under the Upjohn
Company 1992 Stock Option Plan.

      The registrant previously registered 2,009,610,014 shares of common stock
on Form S-4, Registration Statement No. 333-98105; $5,770,649.14 was previously
paid in connection with the filing of Registration Statement No. 333-98105.

      The Pfizer common stock includes Pfizer Preferred Stock purchase rights
which, until events specified in Pfizer's Rights Agreement occur, will not be
exercisable or evidenced separately from the common stock.

                                    PART II.
              INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 3. INCORPORATION OF DOCUMENTS BY REFERENCE

      The following are incorporated by reference:

      o     the Annual Report of Pfizer Inc. on Form 10-K for the year ended
            December 31, 2002,

      o     all other reports we subsequently filed under Sections 13(a) or
            15(d) of the Securities Exchange Act of 1934,

      o     the description of our common stock contained in our Registration
            Statement filed under Section 12 of the Securities Exchange Act of
            1934, including all amendments and reports updating the description,

      o     the Annual Report of Pharmacia Corporation on Form 10-K for the year
            ended December 31, 2002, and

      o     all other reports subsequently filed by Pharmacia Corporation under
            Sections 13(a) or 15(d) of the Securities and Exchange Act of 1934.

      All documents later filed by us under Section 13(a), 13(c), 14, and 15(d)
of the Securities Exchange Act of 1934, before we file a post-effective
amendment that indicates all securities offered have been sold or which
deregisters all securities that have not been sold, will be incorporated by
reference and will be a part of this filing from the date that document was
filed.

ITEM 4. DESCRIPTION OF SECURITIES

      Not applicable.

ITEM 5. INTERESTS OF NAMED EXPERTS AND COUNSEL

      The validity of the securities has been passed upon by Margaret M. Foran,
Esq., Vice President - Corporate Governance and Secretary for the Company. Ms.
Foran beneficially owns Common Stock and options to purchase Common Stock
granted under the Pfizer Inc. Stock and Incentive Plan.

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ITEM 6. INDEMNIFICATION OF DIRECTORS AND OFFICERS

      Section 145 of the General Corporation Law of Delaware permits a
corporation to indemnify any person who is or has been a director, officer,
employee or agent of the corporation or who is or has been serving as director,
officer, employee or agent of another corporation, organization or enterprise at
the request of the corporation, against all liability and expenses (including,
but not limited to, attorneys' fees and disbursements and amounts paid in
settlement or in satisfaction of judgments or as fines or penalties) incurred or
paid in connection with any claim, action, suit or proceeding, whether civil,
criminal, administrative, investigative or otherwise, in which he/she may be
involved by reason of the fact that he/she served or is serving in these
capacities, if he/she acted in good faith and in a manner he/she reasonably
believed to be in or not opposed to the best interest of the corporation and,
with respect to any criminal action or proceeding, had no cause to believe
his/her conduct was unlawful. In the case of a claim, action, suit or proceeding
made or brought by or in the right of the corporation to procure a recovery or
judgment in its favor, the corporation shall not indemnify such person in
respect of any claim, issue or matter as to which such person has been adjudged
to be liable to the corporation for negligence or misconduct in the performance
of his/her duty to the corporation, except for such expenses as the court may
allow. Any such person who has been wholly successful on the merits or otherwise
with respect to any such claim, action, suit or proceeding or with respect to
any claim, issue or matter therein, shall be indemnified as of right against all
expenses in connection therewith or resulting therefrom.

      Pursuant to Article V, Section 1 of our By-Laws, we will indemnify
directors and officers to the fullest extent permitted by applicable law as it
presently exists or is amended. We are insured against actions taken under our
By-Laws and the directors and officers are insured directly at our expense
against such liabilities for which indemnification is not made. We have entered
into agreements with our directors and certain of our officers requiring us to
indemnify such persons to the fullest extent permitted by our By-Laws.


ITEM 7. EXEMPTION FROM REGISTRATION CLAIMED

      Not applicable.


ITEM 8. EXHIBITS

EXHIBIT

 5       --   Opinion and Consent of Margaret M. Foran, Esq., Vice President -
              Corporate Governance and Secretary.


23(i)    --   Consent of KPMG LLP, independent auditors.


23(ii)   --   Consent of PricewaterhouseCoopers LLP, independent accountants.


23(iii)  --   Consent of Deloitte & Touche LLP, independent auditors.


ITEM 9. UNDERTAKINGS

      The Company undertakes:

      (1)   to file, during any period in which offers or sales are being made,
            a post-effective amendment to this registration statement:

            (i)   To include any prospectus required by Section 10(a)(3) of the
                  Securities Act of 1933;

            (ii)  To reflect in the prospectus any facts or events arising after
                  the effective date of the registration statement (or the most
                  recent post-effective amendment) which, individually or in the
                  aggregate, represent a fundamental change in the information
                  set forth in the registration statement;

            (iii) To include any material information about the plan of
                  distribution not already disclosed in the registration
                  statement or any material change to such information in the
                  registration statement;

            provided, however, that paragraphs (1)(i) and (1)(ii) do not apply
            if the registration statement is on Form S-3 or Form S-8 and the
            information required to be included in a post-effective amendment by
            those paragraphs is contained in periodic reports filed by the
            registrant

                                       3


            pursuant to Section 13 or Section 15(d) of the Securities Exchange
            Act of 1934 that are incorporated by reference in the registration
            statement.

      (2)   that, for purposes of determining any liability under the Securities
            Act of 1933, each such post-effective amendment shall be a new
            registration statement relating to the securities offered, and the
            offering of such securities at that time will be viewed as the
            initial bona fide offering.

      (3)   to remove from registration by means of a post-effective amendment
            any of the securities being registered which remain unsold at the
            end of the offering.

      (4)   that, for purposes of determining any liability under the Securities
            Act of 1933, each filing of the registrant's annual report pursuant
            to Section 13(a) or Section 15(d) of the Securities Exchange Act of
            1934 (and, where applicable, each filing of an employee benefit
            plan's annual report pursuant to Section 15(d) of the Securities
            Exchange Act of 1934) that is incorporated by reference in the
            registration statement will be a new registration statement relating
            to the securities offered, and the offering of such securities at
            that time shall be viewed as the initial bona fide offering.

      Insofar as indemnification for liabilities arising under the Securities
Act of 1933 may be permitted to directors, officers and controlling persons of
the registrant under the foregoing provisions, or otherwise, the registrant has
been advised that in the opinion of the Securities and Exchange Commission such
indemnification is against public policy as expressed in the Act and is
unenforceable. In the event that a claim for indemnification against such
liabilities (other than the payment by the registrant of expenses incurred or
paid by a director, officer or controlling person of the registrant in the
successful defense of any action, suit or proceeding) is asserted by such
director, officer or controlling person in connection with the securities being
registered, the registrant will, unless in the opinion of its counsel the matter
has been settled by controlling precedent, submit to a court of appropriate
jurisdiction the question whether such indemnification by it is against public
policy as expressed in the Act and will be governed by the final adjudication of
such issue.

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                                   SIGNATURES

      Under the requirements of the Securities Act of 1933, the Registrant has
reasonable grounds to believe that it meets all of the requirements for filing
on Form S-8 and has caused this Registration Statement to be signed on its
behalf by the authorized signer in The City of New York, State of New York, on
the 16th day of April, 2003.


                                      PFIZER INC

                                      By /s/ HENRY A. MCKINNELL
                                         --------------------------------------
                                         HENRY A. MCKINNELL
                                         Chairman of the Board , Chief Executive
                                         Officer and Director
                                         (Principal Executive Officer)

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

         SIGNATURE                       TITLE                  DATE
---------------------------    ------------------------     ---------------

/s/ HENRY A. MCKINNELL         Chairman of the Board,       April 16, 2003
---------------------------    Chief Executive Officer
(Henry A. McKinnell)           and Director (Principal
                               Executive Officer)


/s/ DAVID L. SHEDLARZ          Executive Vice President     April 16, 2003
---------------------------    and Chief Financial
(David L. Shedlarz)            Officer (Principal
                               Financial Officer)


/s/ LORETTA V. CANGIALOSI      Vice President -             April 16, 2003
---------------------------    Controller (Principal
(Loretta V. Cangialosi)        Accounting Officer)


/s/ MICHAEL S. BROWN           Director                     April 16, 2003
---------------------------
(Michael S. Brown)


/s/ M. ANTHONY BURNS           Director                     April 16, 2003
---------------------------
(M. Anthony Burns)


/s/ ROBERT N. BURT             Director                     April 16, 2003
---------------------------
 (Robert N. Burt)


/s/ W. DON CORNWELL            Director                     April 16, 2003
---------------------------
(W. Don Cornwell)


/s/ WILLIAM H. GRAY, III       Director                     April 16, 2003
---------------------------
(William H. Gray, III)


/s/ CONSTANCE J. HORNER        Director                     April 16, 2003
---------------------------
(Constance J. Horner)

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/s/ WILLIAM R. HOWELL          Director                     April 16, 2003
---------------------------
(William R. Howell)


/s/ STANLEY O. IKENBERRY       Director                     April 16, 2003
---------------------------
(Stanley O. Ikenberry)


/s/ HARRY P. KAMEN             Director                     April 16, 2003
---------------------------
(Harry P. Kamen)


/s/ GEORGE A. LORCH            Director                     April 16, 2003
---------------------------
(George A. Lorch)


/s/ DANA G. MEAD               Director                     April 16, 2003
---------------------------
(Dana G. Mead)


/s/ FRANKLIN D. RAINES         Director                     April 16, 2003
---------------------------
(Franklin D. Raines)


/s/ RUTH J. SIMMONS            Director                     April 16, 2003
---------------------------
(Ruth J. Simmons)


/s/ WILLIAM C. STEERE, JR.     Director                     April 16, 2003
---------------------------
(William C. Steere, Jr.)


/s/ JEAN-PAUL VALLES           Director                     April 16, 2003
---------------------------
(Jean-Paul Valles)

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                                  EXHIBIT INDEX

EXHIBIT

 5     --     Opinion and Consent of Margaret M. Foran, Esq., Vice President -
              Corporate Governance and Secretary.


23(i)  --     Consent of KPMG LLP, independent auditors.


23(ii) --     Consent of PricewaterhouseCoopers LLP, independent accountants.


23(iii)--     Consent of Deloitte & Touche LLP, independent auditors.

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