EXHIBIT 31.1

**CERTIFICATION OF CHIEF EXECUTIVE OFFICER PURSUANT TO SECTION 302 OF THESARBANES-OXLEY ACT OF 2002**

I, Howard Robin, certify that:

|   | 1.     | I have reviewed this quarterly report on Form 10-Q of Sirna Therapeutics, Inc. for the quarter ended June 30, 2003;                                                                                                                                                                                                                         |
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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 ofthe 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 quarterly report;                                            |
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|   | 4.     | The registrant’s other certifying officer(s) and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules13a-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 theregistrant, 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; |
|   |   |                                                                                                                                                                                                                                                                                                                                        | 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 assuranceregarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principals; |
|   |   |                                                                                                                                                                                                                                                                                                                                        | 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 andprocedures, 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 (theregistrant’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(s) and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to theregistrant’s auditors and the audit committee of registrant’s board of directors (or persons performing the equivalent function):                                 |