**Exhibit31.1**

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**CERTIFICATIONBY THE CHIEF EXECUTIVE OFFICER PURSUANT TOSECTION 302 OF THE SARBANES-OXLEY ACT OF 2002**

I, Henry A. McKinnell,certify that:
| 1.     | I have reviewed this report on Form 10-Q of Pfizer  Inc.;                                                                                                                                                                                                                                                      |
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| 2.     | Based on my knowledge, this report does not contain  any untrue statement of a material fact or omit to state a material fact  necessary to make the statements made, in light of the circumstances under  which such statements were made, not misleading with respect to the period  covered by this report; |
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| 3.     | Based on my knowledge, the financial statements, and  other financial information included in this report, fairly present in all  material respects the financial condition, results of operations and cash  flows of the registrant as of, and for, the periods presented in this report;                     |
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| 4.     | The registrant's other certifying officer and I are  responsible for establishing and maintaining disclosure controls and  procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) for the  registrant and have:                                                                                 |
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|   | a)                                                                                                                                                                                                                                                                                                             | Designed such disclosure controls and procedures, or  caused such disclosure controls and procedures to be designed under our  supervision, to ensure that material information relating to the registrant,  including its consolidated subsidiaries, is made known to us by others within  those entities, particularly during the period in which this report is being  prepared; |
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|   | b)                                                                                                                                                                                                                                                                                                             | Evaluated the effectiveness of the registrant's  disclosure controls and procedures and presented in this report our conclusions  about the effectiveness of the disclosure controls and procedures, as of the  end of the period covered by this report based on such evaluation; and |
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|   | c)                                                                                                                                                                                                                                                                                                             | Disclosed in this report any change in the  registrant's internal control over financial reporting that occurred during  the registrant's most recent fiscal quarter that has materially affected, or  is reasonably likely to materially affect, the registrant's internal control  over financial reporting; and |
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| 5.     | The registrant's other certifying officer and I have  disclosed, based on our most recent evaluation of internal control over  financial reporting, to the registrant's auditors and the audit committee of  the registrant's board of directors (or persons performing the equivalent  functions):            |
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|   | a)                                                                                                                                                                                                                                                                                                             | All significant deficiencies and material weaknesses  in the design or operation of internal control over financial reporting which  are reasonably likely to adversely affect the registrant's ability to record,  process, summarize and report financial information; and |
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|   | b)                                                                                                                                                                                                                                                                                                             | Any fraud, whether or not material, that involves  management or other employees who have a significant role in the registrant's  internal control over financial reporting. |
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Date:  May 7, 2004

 
| /s/ Henry A. McKinnell                                                 |
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| Henry A. McKinnell  Chairman of the Board  and Chief Executive Officer |