**Exhibit 31.1**

 

**CERTIFICATIONS**

 

I, William R. Ringo, certify that:

 

1.             Ihave reviewed this quarterly report on Form 10-Q of Abgenix, Inc.;

 

2.             Basedon my knowledge, this quarterly report does not contain any untrue statement ofa material fact or omit to state a material fact necessary to make thestatements made, in light of the circumstances under which such statements weremade, not misleading with respect to the period covered by this quarterlyreport;

 

3.             Basedon my knowledge, the financial statements, and other financial informationincluded in this quarterly report, fairly present in all material respects thefinancial condition, results of operations and cash flows of the registrant asof, and for, the periods presented in this quarterly report;

 

4.             Theregistrant’s other certifying officer and I are responsible for establishingand maintaining 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 ExchangeAct Rules 13a-15(f) and 15d-15(f)) for the registrant and we have:

 

a) designed such disclosure controls andprocedures, or caused such disclosure controls and procedures to be designedunder our supervision, to ensure that material information relating to theregistrant, including its consolidated subsidiaries, is made known to us byothers within those entities, particularly during the period in which thisquarterly report is being prepared;

 

b) designed such internal control over financialreporting, or caused such internal control over financial reporting to bedesigned under our supervision, to provide reasonable assurance regarding thereliability of financial reporting and the preparation of financial statementsfor external purposes in accordance with generally accepted accountingprinciples;

 

c) evaluated the effectiveness of the registrant’sdisclosure controls and procedures and presented in this quarterly report ourconclusions about the effectiveness of the disclosure controls and procedures,as of the end of the period covered by this quarterly report based on suchevaluation; and

 

d) disclosed in this quarterly report any changein the registrant’s internal control over financial reporting that occurredduring the registrant’s most recent fiscal quarter (the registrant’s fourthfiscal quarter in the case of an annual report) that has materially affected,or is reasonably likely to materially affect, the registrant’s internal controlover financial reporting; and

 

5.             Theregistrant’s other certifying officer and I have disclosed, based on our mostrecent evaluation of internal control over financial reporting, to theregistrant’s auditors and the audit committee of registrant’s board ofdirectors (or persons performing the equivalent functions):

 

a) all significant deficiencies and materialweaknesses in the design or operation of internal control over financialreporting which are reasonably likely to adversely affect the registrant’sability to record, process, summarize and report financial information; and

 

b) any fraud, whether or not material, thatinvolves management or other employees who have a significant role in theregistrant’s internal control over financial reporting.

 
| Dated: August 9, 2005 |                                  |
|----------------------------|---------------------------------------|
|                       |                                  |
|                       | /s/ WILLIAM R. RINGO                  |   |
|                       | William R. Ringo                      |
|                       | President and Chief Executive Officer |
|                       | (Principal Executive Officer)         |

 

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