**Exhibit 31.1**
**Certification Under Section 302**
I, Kenneth I. Moch, certify that:
1. I have reviewed this quarterly report on Form 10-Q of Alteon Inc.;
2. Based on my knowledge, this quarterly report does not contain any untrue statement of amaterial 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 periodcovered by this quarterly report;
3. Based on my knowledge, the financial statements, and other financial information included inthis quarterly report, fairly present in all material respects the financial condition, results ofoperations and cash flows of the registrant as of, and for, the periods presented in thisquarterly report;
4. The registrant’s other certifying officers and I are responsible for establishing andmaintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules13a-15(f) and 15d — 15(f)) for the registrant and have:
          a) designed such disclosure controls and procedures, or caused such disclosurecontrols and procedures to be designed under our supervision, to ensure thatmaterial information relating to the registrant, including its consolidatedsubsidiaries, is made known to us by others within those entities, particularlyduring the period in which this report is being prepared;
          b) designed such internal control over financial reporting, or caused suchinternal control 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 external purposes inaccordance with generally accepted accounting principles;
          c) evaluated the effectiveness of the registrant’s disclosure controls andprocedures and presented in this report our conclusions about the effectivenessof the disclosure controls and procedures, as of the end of the period coveredby this report based on such evaluation; and
          d) disclosed in this report any change in the registrant’s internal controlover financial reporting that occurred during the registrant’s most recentfiscal quarter (the registrant’s fourth fiscal quarter in the case of an annualreport) that has materially affected, or is reasonably likely to materiallyaffect, the registrant’s internal control over financial reporting; and
5. The registrant’s other certifying officers and I have disclosed, based on our most recentevaluation of internal control over financial reporting, to the registrant’s auditors and the auditcommittee of the registrant’s board of directors (or persons performing the equivalent function):
          a) all significant deficiencies and material weakness in the design or operation of internalcontrols over financial reporting which are reasonably likely to adversely affect theregistrant’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 havea significant role in the registrant’s internal controls over financial reporting.     Date: May 10, 2005 By: /s/ Kenneth I. Moch        Kenneth I. Moch   President and Chief Executive Officer   (principal executive officer)
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