EXHIBIT31.1

CERTIFICATION

I, Alan Kessman,Chief Executive Officer of Vion Pharmaceuticals, Inc., certifythat:

1.    I have reviewed this annualreport on Form 10-K of Vion Pharmaceuticals, Inc. (the‘‘Registrant’’);

2.    Based on my knowledge, this annual reportdoes not contain any untrue statement of a material fact or omit tostate a material fact necessary to make the statements made, in lightof the circumstances under which such statements were made, notmisleading with respect to the period covered by this annualreport;

3.    Based on my knowledge, thefinancial statements, and other financial information included in thisannual report, fairly present in all material respects the financialcondition, results of operations and cash flows of the Registrant asof, and for, the periods presented in this annual report;

4.    The Registrant's other certifyingofficer and I are responsible for establishing and maintainingdisclosure 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 theRegistrant and have:

a)    Designed suchdisclosure controls and procedures, or caused such disclosure controlsand procedures to be designed under our supervision, to ensure thatmaterial information relating to the Registrant, including itsconsolidated subsidiaries, is made known to us by others within thoseentities, particularly during the period in which this annual report isbeing prepared;

b)    Designed suchinternal control over financial reporting, or caused such internalcontrol over financial reporting to be designed under our supervision,to provide reasonable assurance regarding the reliability of financialreporting and the preparation of financial statements for externalpurposes in accordance with generally accepted accountingprinciples;

c)    Evaluated theeffectiveness of the Registrant's disclosure controls andprocedures and presented in this annual report our conclusions aboutthe effectiveness of the disclosure controls and procedures, as of theend of the period covered by this annual report based on suchevaluation; and

d)    Disclosed in thisannual report any change in the Registrant’s internal controlover financial reporting that occurred during the Registrant’smost recent fiscal quarter (the Registrant’s fourth fiscalquarter) that has materially affected, or is reasonably likely tomaterially affect, the Registrant’s internal control overfinancial reporting;

5.    TheRegistrant's other certifying officer and I have disclosed, basedon our most recent evaluation of internal control over financialreporting, to the Registrant's auditors and the audit committee ofRegistrant's board of directors (or persons performing theequivalent functions):

a)    Allsignificant deficiencies and material weaknesses in the design oroperation of internal control over financial reporting which arereasonably likely to adversely affect the Registrant's ability torecord, process, summarize and report financial information; and

b)    Any fraud, whether or not material, thatinvolves management or other employees who have a significant role inthe Registrant's internal control over financial reporting.

Date:    March  16, 2006

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|   |  | /s/ Alan Kessman                   |
|   |  | Alan KessmanChief ExecutiveOfficer |
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