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                                                                    EXHIBIT 31.1

                                 CERTIFICATIONS

I, Nancy T. Chang, certify that:

         1.   I have reviewed this report on 10-K of Tanox, Inc.;

         2.   Based on my knowledge, this 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 period covered by this report;

         3.   Based on my knowledge, the financial statements, and other
              financial information included in this report, fairly present
              in all material respects the financial condition, results of
              operations and cash flows of Tanox, Inc. as of, and for, the
              periods presented in this report;

         4.   Tanox's other certifying officers 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 Tanox, Inc. 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 Tanox, Inc.'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
                           Tanox, Inc.'s internal control over
                           financial reporting that occurred during
                           Tanox, Inc.'s most recent fiscal quarter
                           that has materially affected, or is
                           reasonably likely to materially affect,
                           Tanox, Inc.'s internal control over
                           financial reporting; and

         5.   Tanox's other certifying officers 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 Tanox, Inc.'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 Tanox, Inc.'s
                           internal control over financial reporting.

Date: March 15, 2004                       By: /s/ Nancy T. Chang
                                               ---------------------------------
                                                   Nancy T. Chang
                                           President and Chief Executive Officer