EXHIBIT 31.1



CERTIFICATION



I, Donald L. Drakeman, President and Chief Executive Officer of Medarex, Inc., certify that:



1. I have reviewed this Annual Report on Form 10-K of Medarex, Inc.;



2. Based on my knowledge, this annual 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 of the circumstances under which such statements were made, not misleading with respect to the periods covered by this report;



3. Based on my knowledge, the financial statements, and other financial information
included in this annual 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 annual report;



4. The registrants other certifying officer and I are responsible for establishing and
maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) for the registrant and have:



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 the registrant, 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) 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 and procedures, as of the end of the period covered by this report based on such evaluation; and



c) 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 (the registrant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



5. The
registrants other certifying officer and I have disclosed, based on our most recent evaluation of internal control over financial reporting, to the registrants auditors and the audit committee of registrants board of directors (or
persons performing the equivalent functions):



a) All significant deficiencies
and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant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 have a significant role in the registrants internal control over financial reporting.



|                     |  |  |  |                                                                    
|-------------------- |  |  |  | -------------------------------------------------------------------
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|Date: March 15, 2004 |  |  |  | /s/    DONALD L. DRAKEMAN                                          
|                     |  |  |  |                                                                    
|                     |  |  |  | President and Chief Executive Officer (Principal Executive Officer)