ABGENIX, INC.

CHANGE OF CONTROL SEVERANCE AGREEMENT

This Change of Control Severance Agreement (the Agreement) is made and entered into effective as of August 30, 2004 (the Effective Date), by and between William R. Ringo (the Employee) and Abgenix, Inc., a Delaware corporation (the Company).  Certain capitalized terms used in this Agreement are defined in Section 1 below.

RECITALS

A.                                   It is expected that the Company from time to time will consider the possibility of a Change of Control.  The Board of Directors of the Company (the Board) recognizes that such consideration can be a distraction to the Employee and can cause the Employee to consider alternative employment opportunities.

B.                                     The Board believes that it is in the best interests of the Company and its shareholders to provide the Employee with an incentive to continue his employment and to maximize the value of the Company upon a Change of Control for the benefit of its shareholders.

C.                                     In order to provide the Employee with enhanced financial security and sufficient encouragement to remain with the Company notwithstanding the possibility of a Change of Control, the Board believes that it is imperative to provide the Employee with certain severance benefits upon the Employees termination of employment following a Change of Control.

AGREEMENT

In consideration of the mutual covenants herein contained and the continued employment of Employee by the Company, the parties agree as follows:

1.             Definition of Terms.  The following terms referred to in this Agreement shall have the following meanings:

(a)                                  Cause.  Cause shall mean (i) any act of personal dishonesty taken by the Employee in connection with his responsibilities as an employee which is intended to result in substantial personal enrichment of the Employee, (ii) Employees conviction of a felony which the Board reasonably believes has had or will have a material detrimental effect on the Companys reputation or business, (iii) a willful act by the Employee which constitutes misconduct and is injurious to the Company, and (iv) continued willful violations by the Employee of the Employees obligations to the Company after there has been delivered to the Employee a written demand for performance from the Company which describes the basis for the Companys belief that the Employee has not substantially performed his duties.

(b)                                 Change of Control.  Change of Control shall mean the occurrence of any of the following events: