<PAGE>
CERTAIN MATERIAL (INDICATED BY AN ASTERISK) HAS BEEN OMITTED FROM THIS DOCUMENT
PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT. THE OMITTED MATERIAL HAS
BEEN FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION.

                                                                   EXHIBIT 10.16

                                 FIRST AMENDMENT
                    TO THE RENEWED DISTRIBUTION AGREEMENT AND
                   THE DISTRIBUTORSHIP ARRANGEMENTS AGREEMENT
                               DATED MAY 2ND, 1997

This Amendment is entered into as of the 4th day of August 2000 by and between
Gen-Probe Incorporated, a Delaware corporation, with its principal place of
business located at 10210 Genetic Center Drive, San Diego, California 92121
("GEN-PROBE") and bioMerieux S.A., a French corporation, having its principal
place of business at Chemin de l'Orme, 69280 Marcy l'Etoile, France
("BIOMERIEUX").

                                    RECITALS

A.    GEN-PROBE and BIOMERIEUX have entered into a Distribution Agreement and a
      Distributorship Arrangements Agreement ("the Agreements") both dated May
      2nd, 1997, under which GEN-PROBE has appointed BIOMERIEUX as its exclusive
      distributor for the sale of certain products in certain specified
      countries.

B.    The Distributorship Arrangements Agreement has been modified twice from
      its date of conclusion, by way of amendments, in order to (i) delete
      Singapore from the list of countries identified as Phase 11 Countries, and
      (ii) to include Poland, a Phase III Country, into the definition of the
      Territory pursuant to Section 1.5 of the Distributorship Arrangement
      Agreement.

C.    The Distribution Agreement has been modified once from its date of
      conclusion, by way of amendment dated February 2 , 1998, in order to (i)
      modify the wording of Section 3.3 of the Distribution Agreement, and (ii)
      to delete Exhibit C to the Distribution Agreement.

D.    The Distribution Agreement and the Distributorship Arrangements Agreement
      are sometimes collectively referred to in this Amendment as "the
      Distribution Agreements."

E.    The original term of the Distribution Agreements have been extended by a
      Renewal Amendment signed by the parties as of November 2, 1999.

F.    GEN-PROBE and BIOMERIEUX have expressed their interest in expanding the
      scope of the Distribution Agreements and have therefore decided to enter
      into this First Amendment to the renewed Distribution Agreements.
<PAGE>
                                    AMENDMENT

Now therefore, in consideration of the mutual commitments set forth below, the
parties hereto agree as follows:

1.    Definitions. Capitalized terms not otherwise defined herein shall have the
      meaning ascribed to them in the Agreements.

2.    The parties mutually agree to amend the Distribution Agreement to
      supplement the Products subject to section 1.5 and Exhibit A thereof by
      including the following as Products at the prices set forth:

<TABLE>
<S>                                                                                   <C>
Mycoplasma Tissue Culture, Non-Isotopic ("MTCNI") .................................   [***]
MTD Controls ......................................................................   [***]
LeaderCheck D......................................................................   [***]
</TABLE>

3.    The parties mutually agree to amend the Distribution Arrangements
      Agreement to expand the definition of Phase III countries as set forth in
      section 1.3 thereof to include the People's Republic of China (including
      Hong Kong) as a Phase III country.

4.    Pursuant to section 1.5 (iii) of the Distributorship Arrangements
      Agreement, the parties hereby mutually agree to designate the following
      Phase III countries as included within the definition of the Territory:
      The People's Republic of China (including Hong Kong); India; Argentina;
      Colombia; Macedonia; Mexico; and Mongolia.

5.    BMX will provide reasonable training to two members of the Chugai Business
      Group in order to educate them with respect to doing business in the
      People's Republic of China. Each party shall bear its own personnel costs
      with respect to this training. Chugai Business Group shall bear all travel
      costs for its employees.

*** Certain information on this page has been omitted and filed separately with
the Commission. Confidential treatment has been requested with respect to the
omitted portions.
<PAGE>
6.    Except as expressly modified hereby, all terms and conditions of the
      renewed Distribution Agreements (as previously amended) shall remain
      unchanged and in full force and effect.

AGREED TO AND ACCEPTED BY:

GEN-PROBE INCORPORATED                             BIOMERIEUX S.A.


By:      /s/ Henry L. Nordhoff                     By:    /s/ Francois Guinot
Name:    Henry L. Nordhoff                         Name:  Francois Guinot
Title:   President & CEO                           Title: Director General