Exhibit 31.1 CERTIFICATION  Certification Pursuant to Rule 13a-14(a) and
15d-14(a) of the Exchange Act  I,
Colin W. Stewart, Chief Executive Officer of CollaGenex Pharmaceuticals, Inc.,
certify that:  1.I have reviewed this Annual Report on Form 10-K
of CollaGenex Pharmaceuticals, Inc.  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.  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.  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:  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; and  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 the financial
statements for external purposes in accordance with generally accepted
accounting principles; and  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  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.  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):  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  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. StewartDated: March 17,
  2008
  
  Colin W. StewartChief Executive Officer