Exhibit 31.1

ADHEREX TECHNOLOGIES INC

CERTIFICATION

I, William P. Peters, Chairman and Chief Executive Officer, certify that:



| | 1. | I have reviewed this quarterly report on Form 10-Q of Adherex Technologies Inc.
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| | 2. | Based on my knowledge, this quarterly 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 quarterly report;
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| | 3. | Based on my knowledge, the financial statements and other financial information included in this quarterly 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 quarterly 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-14 and
15d-14) and we have:
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| | (a) | Designed such disclosure controls and procedures 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 quarterly is being prepared;
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| | (b) | Evaluated the effectiveness of the registrants disclosure controls and procedures as of a date within 90 days prior to filing this quarterly report (the Evaluation
Date); and
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| | (c) | Presented in this quarterly report our conclusions about the effectiveness of the disclosure controls and procedures based on our evaluation as of the Evaluation date;
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| | 5. | The registrants other certifying officer and I have disclosed, based on our most recent evaluation, 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 in the design or operation of internal control which could adversely affect the registrants ability to record, process, summarize and quarterly
report financial data and have identified for the registrants auditors any material weakness in internal controls; 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 controls;
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| | 6. | The registrants other certifying officers and I have indicated in this quarterly report whether or not there were significant changes in internal controls or in other factors
that could significantly affect internal controls subsequent to the date of our most recent evaluation, including any corrective actions with regard to significant deficiencies and material weaknesses.
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Date: May 14, 2009



By:

/s/ William P. PetersWilliam P. PetersChairman and Chief Executive Officer