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| 1.     | I have    reviewed this Quarterly Report on Form 10-Q of CollaGenex Pharmaceuticals,    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)) and internal control over financial    reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) 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)                                                                                                                                                                                                                                                                                                                                                       | Designed    such internal control over financial reporting, or caused such internal    control over financial reporting to be designed under our supervision, to    provide reasonable assurance regarding the reliability of financial reporting    and the preparation of financial statements for external purposes in    accordance with generally accepted accounting principles; |
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|   | c)                                                                                                                                                                                                                                                                                                                                                       | 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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|   | d)                                                                                                                                                                                                                                                                                                                                                       | 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    (the registrant’s fourth fiscal quarter in the case of an annual report) 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. |

|                     | /s/ COLIN W. STEWART       |
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| Dated:    August 9, 2005 | Colin W.    Stewart        |
|                     | Chief    Executive Officer |

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