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                                                                   EXHIBIT 10.23

          Confidential Materials omitted and filed separately with the
         Securities and Exchange Commission. Asterisks denote omissions.

                                    AGREEMENT

         This Agreement (this "Agreement") is made on May 1, 2003 (the
"Effective Date"), by and between IDENIX (CAYMAN) LIMITED, a corporation
organized and existing under the laws of the Cayman Islands ("Idenix"), and
MICROBIOLOGICA QUIMICA E FARMACEUTICA LTDA, a limited liability company
organized under the laws of Brazil ("Microbiologica").

                                    RECITALS

WHEREAS, Idenix, together with its Affiliates, is a biopharmaceutical company
focused on the discovery, development and commercialization of innovative
treatments for life-threatening human infectious diseases, including hepatitis B
virus (REV), hepatitis C virus (HCV) and HIV/AIDS; and

WHEREAS, Microbiologica is a science-based Brazilian company devoted to research
and manufacturing of pharmaceutical compounds; and

WHEREAS, Microbiologica has expertise in process chemistry and manufacture of
antiviral nucleosides and related technologies; and

WHEREAS, upon Idenix's request, Microbiologica: (i) adapted certain core
technologies, created and developed complementary and specific synthetic and
auxiliary procedures to provide Idenix with drug substances, in quantity and
quality, as required for the advancement of preclinical investigations, to
support acute and chronic toxicological studies and pharmaceutical formulation
development, (ii) produced advanced intermediates to be used in the manufacture
of cGMP batches of drug substances for clinical investigations; and (iii)
provided process technology including detailed manufacturing instructions,
references for the main compounds-as well as of their related substances,
detailed analytical procedures and technical support to Idenix and its
contractors for the compounds referred to by Idenix as telbuvidine (LdT),
torcitabine (LdC), and its prodrug derivatives including val-torcitabine; and

WHEREAS, Idenix and Microbiologica desire by this Agreement to formalize, their
arrangement with respect to the compounds mentioned above;

NOW THEREFORE, in consideration of the foregoing premises and the express
promises contained below, Idenix and Microbiolbgica agree as follows:

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                                    ARTICLE I
                                   DEFINITIONS

The following terms as used herein will have the following meaning:

1.1      "Affiliate" will mean any corporation, partnership, or other business
is entity, which is directly or indirectly controlled by Idenix or any entity
which directly or indirectly controls Idenix. As used herein, "control" means
owns directly or indirectly at least thirty percent (30%) of the outstanding
voting securities, or, in the absence of such ownership or n the case of a
non-corporate entity or a non-profit corporation, possession directly or
indirectly of the power to materially influence the direction of the management
and policies of such corporation or non-corporate entity.

1.2      "Agreement" has the meaning set forth in the 1st paragraph hereof.

1.3      "Combination Product" means any pharmaceutical product incorporating
one or more Drug Substance(s) combined with additional active compounds or
ingredients.

1.4      "Drug Substance" means the compounds referred to by Idenix as [**].

1.4      "Microbiologica Technology" means all Inventions, and any other
proprietary information, works of authorship, trade secrets and know-how
relating to the Drug Substances, Products or Combination Products, whether or
not patentable, which have been prior to the Effective Date or are subsequent
thereto discovered, invented, conceived, reduced to practice, authored or
improved by Microbiologica..

1.5      "Patents" means the patent applications and patents issuing therefrom
together with all divisionals, continuations, reissues, reexaminations and
foreign counterparts of such applications or patents covering or relating to the
Microbiologica Technology, including without limitation those patents and patent
applications listed on Exhibit A (as the same may be hereinafter supplemented)
hereto.

1.6      "Product(s)" means a drug product of which the active compound consists
of one or more Drug Substance(s).

1.7      "Valid Claim" means a claim included among the Patents so long as such
claim has not been irrevocably abandoned or held invalid in an unappealable
decision of a court or other authority of competent jurisdiction.

                                   ARTICLE II
                                RESPONSIBILITIES

2.1      Assistance. Microbiologica will support the Idenix projects regarding
[**] if and when rested by Idenix. Idenix has the option to select
Microbiologica for this support or to contract with other suppliers of these
services. If selected, Microbiologica will be compensated for

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providing such support and requested services in accordance with the terms of a
separate specific Agreement. Promptly after the Effective Date and thereafter
from time to time or as reasonably requested by Idenix, Microbiologica will
deliver to Idenix and will permit Idenix to use, copies of such supporting
records and documentation as Microbiologica has in its possession regarding the
manufacture of [**]. Microbiologica will maintain records and documentation
regarding its activities to support the Drug Substance projects.

2.2      Exclusive License and Disclosure of Inventions. Microbiologica hereby
grants Idenix an exclusive, perpetual, irrevocable, sublicenseable,
royalty-free, fully paid up (subject to Section 3.1) worldwide license to use,
manufacture, have manufactured, investigate, develop, import and export, market,
promote, distribute, offer to sell and sell together with the right to
sublicense, Drug Substance, Products and Combination Products using the
Microbiologica Technology and the Patents for the prevention, treatment,
diagnosis and/or control of [**] (collectively, the "Field"). No other license
or right to use the Microbiologica Technology or Patents is granted.

Microbiologica agrees to promptly and fully disclose to Idenix any and all
inventions, works of authorship, discoveries, know-how or improvements
conceived, reduced to practice, discovered, invented, authored, developed or
made by Microbiologica or any of its employees, agents or representatives as a
result of those activities previously undertaken and those which in the future
may be undertaken by Microbiologica with respect to the development of Drug
Substances, Products or Combination Products (collectively, the "Inventions").
All such Inventions, as applied to the said Drug Substances, their Products and
Combination Products, whether or not patentable, shall be included within the
license grant above for no additional compensation to Microbiologica. Inventions
which are patentable will be patented according to Section 2.3 below.
Microbiologica agrees to execute, without charge to Idenix, further documents as
may be reasonably necessary to give effect to this section. Microbiologica
further agrees to use reasonable efforts to work with Idenix to effect such
protections as are available for the Inventions.

2.3      Patent Prosecution and Maintenance. Idenix, after and in consultation
with Microbiologica, will prepare, file, prosecute and maintain the Patents.
Microbiologica agrees to provide Idenix, or its counsel, with copies of
documents, records, correspondence or other information Microbiologica receives,
prepares or causes to be prepared in connection with the preparation,
prosecution and maintenance of the Patents. Idenix, upon ninety (90) days
advance written notice to Microbiologica, may advise Microbiologica that Idenix
no longer desires to file, prosecute or maintain one or more of the Patents. In
such event, Microbiologica may request that Idenix assign to Microbiologica all
its rights in such Patents. In that case, Idenix agrees to provide
Microbiologica, or its counsel, with copies of documents, records,
correspondence or other information necessary to effect the assignment of the
rights of Idenix in such Patent(s) to Microbiologica.

2.4      Patent Enforcement. Idenix may, itself or through a designee, and in
its sole discretion, take any actions to protect the Patents from infringement
in the Field and to protect the Microbiologica Technology from unauthorized use
in the Field. Idenix or its designee may institute suit or take other action to
so protect the Patents and the Microbiologica Technology in the Field in its
name and/or in Microbiologica's name. Microbiologica shall promptly notify

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Idenix or its designee if Microbiologica becomes aware of any possible
infringement of the Patents in the Field or unauthorized use of the
Microbiologica Technology in the Field.

2.5      Invalidity Claims. Microbiologica shall promptly notify Idenix or its
designee if Microbiologica becomes aware that any third party asserts that any
Patent is invalid or otherwise unenforceable (an "Invalidity Claim").
Microbiologica shall cooperate with Idenix or its designee in preparing and
formulating a response, and in taking other steps reasonably necessary to
respond, to such Invalidity Claim. Microbiologica shall not settle or compromise
any Invalidity Claim without the consent of Idenix or its designee.

2.6      Cooperation. Microbiologica shall cooperate with Idenix or its designee
with respect to any actions taken pursuant to Sections 2.4 or 2.5 to the extent
reasonably possible, including the joining of suit if necessary or desirable.

                                   ARTICLE III
                             FINANCIAL ARRANGEMENTS

3.1      License. In consideration for the license of the Microbiologica
Technology and the Patents, Idenix will pay or cause to be paid to
Microbiologica the aggregate amount of [**] Dollars (US$[**]) in accordance with
this Section 3.1. The first payment in the amount of US$[**] million will be
made on [**] and subsequent payments in the amount of US$[**] million will be
made beginning [**] and continuing annually thereafter on each [**] or the next
business day until ending on [**].

3.2      Patent Prosecution, Maintenance and Enforcement Costs. Idenix will bear
all costs relating to the prosecution, maintenance, and to the extent Idenix
determines to be necessary, enforcement of Patents in accordance with the
exercise of Idenix's rights pursuant to Sections 2.3, 2.4 and 2.5.

                                   ARTICLE IV
                         REPRESENTATIONS OF THE PARTIES

4.1      Representations and Warranties of Idenix. Idenix represents and
warrants that it is fully authorized to enter into this Agreement and that by
entering into this Agreement Idenix is not in breach of any provision of any
other agreement. Idenix further represents and warrants that it has, prior to
the Effective Date, maintained in confidence the Microbiologica Technology.

4.2      Representations and Warranties of Microbiologica. Microbiologica
represents and warrants that it is fully authorized to enter into this Agreement
and that by entering this Agreement Microbiologica is not in breach of any
provision of any other agreement. Microbiologica further represents and warrants
that it has, prior to the Effective Date, maintained in confidence the
Microbiologica Technology, except to the extent reasonably necessary to file the
patent application specified in Exhibit A.

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                                    ARTICLE V
                              ADDITIONAL PROVISIONS

5.1      Confidentiality. Neither Idenix or Microbiologica shall, without the
express written consent of the other party, for any reason or at any time during
the term of this Agreement, disclose to third parties any information disclosed
in the Microbiologica Technology. This obligation of nondisclosure shall not
include third parties that are Affiliates of Idenix or Microbiologica provided
that such Affiliates are subject to provisions with disclosing party that are
the same or substantially the same as those included in Sections 5.1 and 5.2)
and shall not extend to information:

         (a)      which was in the public domain prior to the date of this
                  Agreement, as evidenced by documents published prior to such
                  disclosure;

         (b)      which, after the date of this Agreement, comes into the public
                  domain through no fault of a party to this Agreement;

         (c)      which is disclosed to either party to this Agreement by a
                  third party having legitimate possession of the information
                  and the unrestricted right to make such disclosure; and

         (d)      which is disclosed in the Patents after publication of such
                  Patents.

5.2      Exceptions to Obligations of Confidentiality. Notwithstanding the
provisions of Paragraph 5.1 above, and to the extent necessary:

         (a)      a party may disclose and use the other party's information for
                  purposes of securing the registration of, and of governmental
                  approval to market, pursuant to this Agreement, any Drug
                  Substance, Product, and/or Combination Products;

         (b)      a party may disclose and use the other party's information
                  where the disclosure and use of such will be necessary to the
                  procurement of patent protection, pursuant to this Agreement,
                  for any Drug Substance, Product, ,and/or Combination Products;

         (c)      a party may disclose and use the other party's information to
                  the extent that it is necessary to aid in the development and
                  commercialization, pursuant to this Agreement, of any Drug
                  Substance, Product, and/or Combination Products provided that
                  any such disclosure of the disclosing party's information
                  shall be in confidence and subject to provisions the same, or
                  substantially the same, as those in Paragraph 5.1 hereof;

         (d)      a party may disclose the other party's information to the
                  extent required by applicable law; and

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         (e)      Microbiologica may disclose the Microbiologica Technology to a
                  third party to commercialize the Microbiologica Technology in
                  areas other than the Field, provided that any such disclosure
                  of the Microbiologica Technology will be in confidence and
                  subject to provisions the same or substantially the same, as
                  those in Paragraph 5.1 hereof.

5.3      Term; Termination. Unless sooner terminated by mutual agreement of the
parties the term of this Agreement will continue until the later of the: (1) the
date of expiration of the last Valid Claim covering Patent; or (2) twenty years
after the execution of this Agreement. In the event of a termination or
expiration of this Agreement, the provisions of Articles II and III shall
survive unless explicitly agreed to the contrary by the parties. Notwithstanding
the foregoing, the obligations of confidentiality set forth in Section 5.1 and
5.2 shall survive the termination of this Agreement.

5.4      NO LIABILITY. MICROBIOLOGICA WILL NOT BE LIABLE TO IDENIX, IDENIX'
CUSTOMERS, SUB LICENSEES, MARKETING PARTNERS OR AFFILIATES FOR SPECIAL,
INCIDENTAL, INDIRECT, OR CONSEQUENTIAL DAMAGES RESULTING FROM DEFECTS IN THE
DESIGN, TESTING, LABELING, MANUFACTURE, OR OTHER APPLICATION OF PRODUCTS OR
COMBINATION PRODUCTS DEVELOPED, DESIGNED, TESTED, MANUFACTURED, MARKETED,
SUBLICENSED, OR SOLD PURSUANT TO THIS AGREEMENT.

         IDENIX WILL NOT BE LIABLE TO MICROBIOLOGICA, ITS DIRECTORS, OFFICERS,
EMPLOYEES OR AFFILIATES FOR SPECIAL, INCIDENTAL, CONSEQUENTIAL, EXEMPLARY,
PUNITIVE, MULTIPLE OR OTHER INDIRECT DAMAGES, OR FOR LOSS OF PROFITS, LOSS OF
DATA OR LOSS OF USE DAMAGES, ARISING OUT OF THIS AGREEMENT, EVEN IF IDENIX HAS
BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES OR LOSSES.

5.5      Binding Nature of Agreement; Amendments. All of the terms and
provisions of this Agreement will be binding upon and inure to the benefit of
and be enforceable by the respective successors and assigns of the parties
hereto. This Agreement may not be changed or modified except by a written
amendment executed by an authorized representative of each Party. Microbiologica
may assign its rights and obligations under this Agreement, in whole or in part,
without the prior written consent of Idenix. Idenix may assign its rights and
obligations under this Agreement and the licenses granted hereunder, in whole or
in part, without the consent of Microbiologica to any person or entity or to an
Affiliate or to a person or entity which acquires all or substantially all of
the assets or business of Idenix, whether by sale, merger or otherwise.

5.6      Governing Law. This Agreement will be governed by the laws of the State
of New York, U.S.A. excluding its conflicts of laws principles.

5.7      Counterparts, Headings and Exhibits. This Agreement may be executed in
two or more counterparts, each of which will be deemed an original, but all of
which together will constitute one and the same instrument. The headings used in
this Agreement are for convenience only and are not to be considered in
construing or interpreting any term or provision of this Agreement.

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5.8      Dispute Resolution. Any disputes under this Agreement not resolved by
negotiation between the parties will be submitted to resolution pursuant to
binding arbitration conducted under the Commercial Arbitration Rules of the
American Arbitration Association by three arbitrators, one appointed by
Microbiologica, one appointed by Idenix and one appointed by the two arbitrators
appointed respectively by Microbiologica and Idenix. The arbitration will take
place in New York, New York and the decision of the arbitrators will be
enforceable but not appealable in any court of competent jurisdiction.

5.9      Independent Contractors. It is understood and agreed that the
relationship between the parties hereunder is that of independent contractors
and that nothing in this Agreement shall be construed as authorization for
either party to act as agent for the other.

5.10     Severability. In the event that any provision of this Agreement is held
to be unenforceable because it is invalid or in conflict with any law of any
relevant jurisdiction, the validity of the remaining provisions shall not be
affected, and the rights and obligations of the parties shall be construed and
enforced as if the Agreement did not contain the particular provisions held to
be unenforceable, unless such construction would materially alter the meaning of
this Agreement.

5.11     No Strict Construction. This Agreement has been prepared jointly and
shall not be strictly construed against any Party.

         IN WITNESS WHEREOF, the parties hereto have executed this Agreement on
the date first written above.

IDENIX (CAYMAN) LIMITED                         MICROBIOLOGICA, LTDA

By: /s/Jean-Pierre Sommadossi, Ph.D.            By: /s/ Jaime A. Rabi, Ph.D.
    --------------------------------------          ----------------------------
Jean-Pierre Sommadossi, Ph.D.                   Jaime A. Rabi, Ph.D.
Director                                        Director

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                                    EXHIBIT A

                                     Patents

[**].

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