UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION

                              WASHINGTON, DC 20549

                                   FORM 10-Q/A
                                 Amendment No. 1

[x]   Quarterly report pursuant to Section 13 or 15(d) of the Securities
      Exchange Act of 1934

                For the quarterly period ended March 31, 2000 or

[_]   Transition report pursuant to Section 13 or 15(d) of the Securities
      Exchange Act of 1934

    For the transition period from _______________ to ________________

                        COMMISSION FILE NUMBER 000-30231

                                   TANOX, INC.
             (Exact Name of Registrant as Specified in Its Charter)

            DELAWARE                                  76-0196733
(State or Other Jurisdiction of                     (IRS Employer
Incorporation of Organization)                     Identification No.)

      10301 STELLA LINK, SUITE 110
             HOUSTON, TEXAS                                 77025-5497
(Address of Principal Executive Offices)                    (Zip Code)

                                 (713) 664-2288
              (Registrant's Telephone Number, Including Area Code)

      Indicate by check mark whether the registrant: (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days.

(1)   Yes  [X]   No  [ ]                 (2)   Yes  [ ]   No  [X]

      As of May 11, 2000, the registrant had 42,541,123 shares of Common Stock
issued and outstanding.

      Following herewith is the Signature page of Registrant's Form 10-Q,
originally filed on May 12, 2000. The Signature page has been revised to include
the conformed signatures of Nancy T. Chang and David Duncan, Jr., which were
inadvertently omitted from Registrant's original filing.

                                   SIGNATURES

      Pursuant to the requirements of the Securities Exchange Act of 1934, the
registrant has duly caused this report to be signed on its behalf by the
undersigned thereunto duly authorized.

                                      TANOX, INC.

Date: May 12, 2000                    By: /s/ Nancy T. Chang
                                      Nancy T. Chang, Chief Executive Officer

Date: May 12, 2000                    By: /s/ David Duncan, Jr.
                                      David Duncan, Jr., Chief Financial Officer

                                   SIGNATURES

      Pursuant to the requirements of the Securities Exchange Act of 1934, the
registrant has duly caused this report to be signed on its behalf by the
undersigned thereunto duly authorized.

                                      TANOX, INC.

Date: May 15, 2000                    By: /s/ Nancy T. Chang
                                      Nancy T. Chang, Chief Executive Officer

Date: May 15, 2000                    By: /s/ David Duncan, Jr.
                                      David Duncan, Jr., Chief Financial Officer