Document:

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                                                                    EXHIBIT 10.1

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                              ADMINISTRATIVE LEASE
                               HOTEL D'ENTREPRISES
                                    CAP GAMMA

                     CHAPTER I: SPECIAL TERMS AND CONDITIONS

BETWEEN:

SOCIETE D'EQUIPEMENT DE LA REGION MONTPELLIERAINE, "SERM", a French public
sector "mixed economy" corporation (societe anonyme d'economie mixte), the
registered capital of which is EUR 5,894,000, the registered office of which is
located in Montpellier (34000), Hotel de Ville, and its offices located 45 Place
E.Granier, Etoile Richter MONTPELLIER Cedex 2 (34960) identified with the SIREN
under number 462800160 and registered with the Registry of Commerce and
Companies (Registre du Commerce et des Societes) of Montpellier.

herein represented by its General secretary Mr. Andre LE GRAVEREND, under
authority granted to him by the General Manager (Directeur General), Mr. Eric
BERARD having himself the authority granted by SERM's Board of Directors at a
Meeting held on 2 October 2002

Hereinafter called the "LANDLORD" OR "SERM"

                                                        PARTY OF THE FIRST PART,
AND:

IDENIX SARL the registered capital of which is EUR 1 000 000 the registered
office of which is in MONTPELLIER, 170, rue Leon BLUM, 34000, FRANCE registered
with the Registry of Commerce and Companies (Registre du Commerce et des
Societes - RCS) of Montpellier under number 419 909 148, herein represented by
Jean- Pierre SOMMADOSSI, CEO of IDENIX PHARMACEUTICALS Inc. and Managing
Director (Gerant) of SARL IDENIX,

Hereinafter called the "TENANT"

                                                       PARTY OF THE SECOND PART,
AND

The COMMUNAUTE D'AGGLOMERATION DE MONTPELLIER (Metropolitan Area Authority of
Montpellier), herein represented by Monsieur Georges FRECHE, President of
Communaute d'Agglomeration de Montpellier, acting under authority granted by a
resolution of the Conseil de la Communaute d'Agglomeration (Board of the
Metropolitan Area Authority) adopted on December 23rd, 2004 and published on
December 29th,2004.

Hereinafter called the "INTERVENOR"

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                                                        PARTY OF THE THIRD PART,

RECITALS:

SERM owns a lot with of an area of approximately 11,100 m(2), recorded in the
land records at section AA 38 partie, located in the ZAC EUROMEDECINE II
development zone in the Town of Grabels (34 790) , 1682, rue de la Valsiere.

The ZAC "Parc Euromedecine" zone was created on 6 November 1986, and the
completion application was approved on 24 February 1988.

Under Articles L 300-1 to L 300-4 et seq. of the Urban Planning and Zoning Code,
the District decided to entrust to Societe d'Equipement de la Region
Montpellieraine (SERM) the completion of part of the development work for the
ZAC Parc Euromedecine II zone, on the terms and conditions set forth in an
Agreement, dated 25 March 1988, filed at the Office of the Prefect (Prefecture)
on 30 March 1988, together with its subsequent amendments.

Following the adoption of the Law of 13 December 2000 (SRU), a public
development agreement (convention publique d'amenagement) substituted therefor
and repeating all of the above-described agreement was signed on 1st October
2001.

The District having been transformed into the Metropolitan Area Authority
(Communaute d'Agglomeration) of Montpellier, as from 1st August 2001, by Order
of the Office of the Prefect n(degree)2001-I-3216 dated 30 July 2001,
development of such zone is being conducted under the direction and control of
the Metropolitan Area Authority (Communaute d'Agglomeration) at its financial
risk.

The lack of space for specialized companies led the Metropolitan Area Authority
(Communaute d'Agglomeration) of Montpellier to implement alternative approaches
based on private initiative to support development of business activities, the
creation, and the stabilization of employment.

By an amendment n(degrees)1 to the Public Development Agreement (convention
publique d'amenagement), dated 30 July 2002, the Metropolitan Area Authority
(Communaute d'Agglomeration) of Montpellier asked SERM to analyze, build, and
manage a specific real estate complex called CAP GAMMA, intended for use by
companies specializing in biotechnology and pharmaceutical chemistry.

Under such public development agreement, SERM is required to give notice of any
potential leasing candidate to, and obtain the approval of, the Metropolitan
Area Authority (Communaute d'agglomeration) of Montpellier prior to the lease's
effective date.

IDENIX has made known that it is particularly interested in the space located in
such Zone. It plans eventually to consolidate there the three Montpellier
facilities and develop its business, projecting to have a headcount in 2007 of
80 employees. It is planning significant investments in this connection to
prepare the space that is the subject matter of this Lease. In this connection,
it has negotiated with SERM the special terms and conditions of rent.

On 17 December 2004, the parties entered into a Bilateral Offer of
Administrative Lease under which the parties agreed to ratify such offer by
entering into this Lease.

It is hereby stated that IDENIX PHARMACEUTICALS, INC, which indirectly owns 100%
of IDENIX SARL's registered capital, has agreed to act as joint and several
guarantor to secure payment of all amounts due by IDENIX SARL in connection with
this Administrative Lease (see, Exhibit n(degrees)13).

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INTERVENTION OF THE  COMMUNAUTE D'AGGLOMERATION DE MONTPELLIER

Monsieur Georges FRECHE, President of Communaute d'Agglomeration de Montpellier,
acting under authority granted by a resolution of the Conseil de la Communaute
d'Agglomeration (Board of the Metropolitan Area Authority), dated December 23rd,
2004 and under the public development agreement (convention publique
d'amenagement), dated 1st October 2001, amended by Amendment n(degrees) 1
thereto, dated 30 July 2002, who stated, in his official capacity, that he
agreed to and accepted the terms and conditions hereof and to be substituted for
Societe d'Equipement de la Region Montpellieraine (S.E.R.M.) in the event of
implementation of the provisions set forth in Part V of the public development
agreement (convention publique d'amenagement) "Legal and Financial Terms and
Conditions on Expiration of the Public Development Agreement" ("Dispositions
juridiques et financieres a l'expiration de la convention publique
d'amenagement"), the real estate assets and rights that are the subject matter
of this Administrative Lease constituting assets that are to revert to and/or be
repossessed by the Communaute d'Agglomeration de Montpellier.

Such terms and conditions are the basis for this "Lease" having the character of
an administrative agreement and, therefore, not being governed by Articles L
145-1 et seq. of the Code of commerce and the unabrogated provisions of Decree
n(degrees) 53-960 dated 30 September 1953 relating to commercial leases.

Even though this agreement does not constitute a lease, strictly speaking, it is
nevertheless called a "Lease", and the terms "rent, lease/rental, landlord,
tenant, etc." shall be used, without the use of such terms constituting a basis
for defining the legal character of this Agreement, which, notwithstanding such
terminology, is, and shall remain, an administrative agreement.

NOW, THEREFORE, THE PARTIES HERETO HEREBY AGREE AS FOLLOWS:

1.    ADDRESS

      a)    Address of the property: ZAC EUROMEDECINE II, 1682 rue de la
            Valsiere, GRABELS (34790)

      b)    Address for payment: SERM, Immeuble "Etoile Richter" 45 place Ernest
            Granier CS 29502 34960 MONTPELLIER Cedex 2

2.    DESCRIPTION AND DATES OF PROGRESSIVE AVAILABILITY OF THE RENTED SPACE

This Lease shall apply to a total usable area, after outfitting of the private
areas, of 3271.60 m(2) at the end of the Tenant's progessive assumption of
possession in the building (A Building) pursuant to the schedule set forth in
the table annexed hereto (Exhibit 1):

1/  FROM 15 APRIL 2005 TO 31 JULY 2005: 387.60 M(2) of laboratory space on
    level N+3 (lot A/3-1)

2/  FROM 1 AUGUST 2005 TO 31 AUGUST 2006: 407.80 m(2) of laboratory space on
    level N+3 (lot A/32) + 147 m(2) of technical space on the ground floor
    (rez-de-chaussee) (lot A/0- 7), i.e., A TOTAL OF 942.40 M(2)

3/  FROM 1 SEPTEMBER 2006 TO 30 NOVEMBER 2006: 795.40 m(2) of offices on level
    N+1 (lot A/1-1), i.e., A TOTAL OF 1737.80 M(2).

4/  FROM 1 DECEMBER 2006 TO 31 MARCH 2007: 795.40 m(2) of laboratory space on
    level N+2 (lot A/2-1) , including 192 m(2) of laboratory space and unused
    reserves, i.e., A TOTAL OF 2533.20 M(2).

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5/  BEGINNING ON 1 APRIL 2007: balance of the ground floor, i.e., 394 m(2)
    (lot A/0-6) + common area taken over as private area on levels 0 to N+3
    representing a total area of 344.40 m(2), i.e., A TOTAL OF 3271.60 M(2).

There shall be attributed to the Tenant a number of outside parking spaces in
proportion to the area rented that are non-private (on space for each 50m(2) of
usable area).
In the end, the Tenant shall have 56 parking spaces.
An additional 24 outside parking spaces shall be completed by the Landlord and
made available to the Tenant upon completion of B Building, covered by the 2nd
phase of the CAP GAMMA program tentatively scheduled for no later than the end
of 2007.

3.    REFERENCE DATE

Effective date of this Lease:  15 APRIL 2005
As provided under Article 3.4 of the Bilateral Offer of an Administrative Lease,
however, since the effective date is subject to the completion a minima of the
technical conditions, except for finishing work, i.e., the compressed air
system, the gas system, the electrical system, the supply of cold water,
elimination of waste water, floor coverings, computer and telephone cabling,
fire detection and prevention system NO LATER THAN 15 APRIL 2005, the effective
date of the lease may be delayed until actual completion of the technical
conditions, except for finishing work.

4.    INTENDED USE

The Tenant shall use the above-described space for offices and laboratories for
the purpose of conducting business relating to pharmaceutical research,
scientific research, manufacture, marketing, and sale of pharmaceutical
products.

5.    TAX TREATMENT:  V.A.T. presently applicable:  19.6%

6.    ANNUAL BASE RENT

The annual Base Rent (excluding taxes and charges) shall be calculated on the
basis of EUR 210 (excluding taxes)/m(2) value as of November 2004, INSEE Cost of
Construction index for the 2nd quarter 2004, i.e., 1267.

The base rent, excluding taxes and charges, however, shall be progressive based
on the availability of the space and calculated in proportion to the actual time
of occupancy (au prorata temporis), i.e.:

-     From 15 April 2005 to 31 July 2005: (EURO) 23 740.50 value as of November
      2004, ICC (INSEE Cost of Construction Index) for the 2nd quarter 2004,
      i.e., 1267

-     From 1 August 2005 to 31 August 2006: (EURO) 214 396 value November 2004,
      ICC for the 2nd quarter 2004, i.e., 1267

-     From 1 September 2006 to 30 November 2006: (EURO) 91 234.50 value November
      2004, ICC for 2nd quarter 2004, i.e., 1267

-     From 1 December 2006 to 31 March 2007: (EURO) 177 324 value November 2004,
      ICC for the 2nd quarter 2004, i.e., 1267

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-     From 1 April 2007 to 31 December 2007: (EURO) 375 000 value November 2004,
      ICC for the 2nd quarter 2004, i.e., 1267.

-     From 1 January 2008: fixed annual rent (excluding taxes and charges) of
      (EURO) 500 000 value November 2004, ICC for the 2nd quarter 2004, i.e.,
      1267.

Deposit for charges as from the time the space is made available of EUR 45 (all
taxes included) TTC./m(2) (usable space) /year, on the basis of the VAT rate in
effect (19.6%).

Periodicity of payment:  quarterly in advance.

Payment of the first installment upon signature of this Lease.
Means of payment : by Bank transfer

7 .   OUTFITTING WORK FOR THE PRIVATE AREAS

The Landlord agrees to complete the outfitting work described in Exhibit 3,
according to the schedule set forth in such Exhibit.

Since the Landlord has agreed to be responsible for the outfitting work for the
private areas allowing the Tenant to move in, it is mutually agreed that the
cost of the outfitting of the private areas, completed by the Landlord at the
Tenant's request, is incorporated in its annual rent. If this Lease should be
terminated prior to the end of the twelfth year, regardless of the reason
therefor, the Tenant agrees to refund to the Landlord the residual value of the
time remaining until the twelfth year of the cost of the work initially
completed on its behalf, set forth in Exhibit 3.

8 .   TENANT'S INVESTMENT PROGRAM

In respect of the investment program in material and equipment (specific
equipment and furnishings) set forth in Exhibit 4 hereof, that the Tenant agrees
to undertake progressively in the space made available to it, the Landlord
agrees to indemnify the Tenant for the residual net book value of such equipment
only in the event of termination for generally applicable reasons (pour motif
d'interet general) prior to expiration of a period of 12 years.

9.    SECURITY DEPOSIT

3 months' rent (excluding taxes) for period 1, i.e.: (EURO) 20 349 payable upon
signature of this Lease. The Landlord acknowledges having received such security
deposit upon signature of the Offer of Lease between the parties dated 16
December 2004 and to retain it as provided under this Article. For the period
from 1 January 2006 to 1 January 2007, as an exception to Article VI 5 of the
General Terms and Conditions, the parties agree to a proportional adjustment of
the security deposit on the basis of the amount of rent in effect as of 1st
January of the calendar year.

10.   ANNUAL INDEXATION

Date of revision: anniversary of the Lease's effective date, i.e., 15 April of
each year. Base Index: INSEE index of the cost of construction for the 2nd
Quarter 2004, i.e., 1267.

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11.   APPROVAL OF THE COMMUNAUTE D'AGGLOMERATION DE MONTPELLIER

The Tenant's application has been approved by a resolution of the Board of the
Montpellier Metropolitan Area Authority (Conseil de la Communaute
d'Agglomeration de Montpellier) adopted on December 23rd, 2004 filed with the
Office of the Prefect on December 23rd, 2004 and notified to the Tenant on
December 29th, 2004

12 .  AMENDMENT OF THIS LEASE

Any amendment to the terms and conditions set forth in this Lease and the
Exhibits hereto (area, dates of availability of the space, etc.) shall be set
forth in an amendment.

13.   INSPECTION (ETATS DES LIEUX)

Since the Tenant will take possession gradually, an inspection (etat des lieux),
the date of which shall be mutually agreed, shall be made in the presence of all
parties (contradictoirement) by the parties at each stage of availability of the
space. It is hereby stated that each inspection (etat des lieux) shall be made
no later than the date of each due date for gradual availability, on the basis
of the schedule set forth in Article 2 hereinabove.

14.   INCONSISTENCY BETWEEN THE SPECIFIC TERMS AND CONDITIONS AND THE GENERAL
      TERMS AND CONDITIONS

The parties hereby represent and warrant that these specific terms and
conditions shall form an integral part of the general terms and conditions
annexed hereto. In the event of any conflict or inconsistency between them, the
specific terms and conditions shall prevail.

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                          CHAPTER II: GENERAL TERMS AND
                                   CONDITIONS

The Landlord hereby leases to the Tenant, which accepts, the premises described
in Chapter I Art. 2, "special terms and conditions".

ARTICLE I -- DESCRIPTION

The Tenant hereby represents and warrants that it is completely familiar with
the premises, without it being necessary to provide a more complete description
thereof than the one set forth in Chapter I Art. 2 at Tenant's request and to
accept them "as is" in the state in which they are found, are extended, and
exist, with all dependencies and appurtenances thereto.

It is hereby stated that any discrepancy between the measurements and the areas
set forth in this Agreement, or resulting from the floor plan annexed hereto and
the actual dimensions of the premises shall not be grounds for any reduction or
increase in rent, and the Parties rely on the consistency of the premises as
they exist.

The Parties expressly agree that the premises rented hereby constitute an
indivisible whole.

ARTICLE II -- TERM

This lease is being made and accepted for a term of TWELVE (12) FULL AND
CONSECUTIVE YEARS that will begin as of the effective date set forth in Chapter
I Art. 3.

The Landlord and the Tenant, however, shall have the right to vacate and
terminate at the end of 6 (six) years and at any time between the 6th and the
12th year, contingent on advising the other party of its intention in this
regard at least 12 (twelve) months in advance by registered letter, return
receipt requested.

The Landlord shall only have the right to rely on reasons of general interest,
or, in the event of breach by the Tenant of its agreements made at the time of
its application, set forth in the exhibit hereto and which forms an integral
part hereof.

Upon expiration, and unless otherwise mutually agreed by the parties, this
Agreement shall no longer be effective as a matter of right (de plein droit),
and the occupant shall not have any right in any event to any claim for renewal.

The presence of the occupant in the premises after expiration, in particular,
shall not give rise to any right of any kind to renew.

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ARTICLE III - INSPECTION (ETAT DES LIEUX)

An inspection (etat des lieux) shall be conducted and a report thereof made in
the presence of all parties (contradictoirement) at the time the Tenant takes
possession. If such inspection and report are not made, because the Tenant fails
to appear, the premises shall be deemed rented as new. The inspection and report
shall be made at the Tenant's expense.

ARTICLE IV - INTENDED USE

The Tenant shall use the premises rented hereby exclusively as set forth in
Chapter I Art. 4, quietly and in compliance with Articles 1728 and 1729 of the
Civil Code.

ARTICLE V -  CHARGES AND CONDITIONS

This Lease is made on ordinary charges and terms and conditions of law and
including, but not limited to, those set forth hereinafter, which the Tenant
agrees to perform exactly and without any right to any indemnity, or reduction
in rent, as hereinafter provided.

1- GENERAL TERMS AND CONDITIONS OF POSSESSION

The Tenant shall take the rented premises in their present state, as set forth
in Chapter I Art. 2, et seq. with the inspection and report thereon (etat des
lieux) described in Chapter I Art. 13, all installation and interior decoration
work to be at its expense, except for outfitting work set forth in Chapter I
Art. 7 hereinabove, without any right to require any compensation or recovery
for taking possession, nor during the term of the Lease. Independently, it shall
be responsible for ensuring all repairs, maintenance, cleaning, that may be
necessary for such premises during the term of the Lease. The Landlord shall
remain responsible for major repairs, as defined in Article 606 of the Civil
Code.

The Tenant hereby acknowledges that the premises rented hereby comply with the
intended use thereof under the Lease.

It shall be personally responsible, as from the date hereof, during the entire
term of this Lease, for the maintenance thereof, as provided by, and in light
of, all administrative regulations and policies applicable to such premises,
given the operations to be conducted therein.

It shall comply with all orders and recommendations from the Office of the Labor
Inspector (Inspection du Travail), the Occupational Safety and Health
Commissions (Commissions d'Hygiene et de securite), and, more generally, all
relevant governmental authorities.

It shall ensure that the Landlord not be disturbed, or any claim made against
it, in this connection.

It shall comply with all charges and terms and conditions set forth in any
document applicable to the real estate complex.

The Tenant shall take all precautions so that the conduct of its businesses does
not interfere with, or bother, in any way the maintenance, quiet enjoyment, or
proper appearance and maintenance of the building, and it shall take any and all
precautions to assure its liability in this regard.

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The Tenant shall not have any right to a reduction in rent or indemnity in the
event of interruption or reduction, even for a prolonged period of time, of
common services, such as water, electricity, telephone, heat, compressed air,
gas, etc. To the extent it has been made aware thereof, the Landlord shall be
responsible for advising the Tenant of such interruptions or reductions fifteen
(15) days in advance thereof in the event of a reduction forecast to last longer
than three (3) days.

It shall not have the right to deposit or leave in the common areas of the
building, which shall always be kept free for access.

It shall use the elevators only in compliance with the builder's instructions,
and the Landlord shall not be liable for any accidents that may occur as a
result of failure to comply with such instructions.

2- WORK - INSTALLATIONS - OUTFITTING

The cost of specific outfitting work performed by the Landlord at the Tenant's
request shall be incorporated in the contractual rent, as set forth in Chapter I
Art. 7.

The Tenant shall agree, without any claim for indemnity or reduction of rent
therefor, to allow and permit to occur any repair, renovation, reconstruction,
or leveling, enlargement and other work that the Landlord may undertake, or
cause to be undertaken, during the term of this Lease to the rented premises, as
well as with respect to the property of which they form a part, regardless of
the character or length thereof, even if they last longer than forty days, by
exception to Article 1724 of the Civil Code. The Landlord agrees, however, to do
everything possible so that such work shall be the least disruptive possible to
Tenant's operations.

The Tenant shall agree, without any claim for indemnity or reduction of rent
therefor, to allow and permit to occur any construction work, as well as
outfitting, relating to the second building of the CAP GAMMA program.

It shall likewise submit to all work that may be performed in the exterior
common areas, to the public thoroughfares, or in neighboring buildings, even
though some disturbance results therefrom to its operations and without any
recourse or claim against the administration, the contractors of the work, or
the neighboring owners, if any, without thereby waiving any rights it may have
under generally applicable rules of law relating to liability.

The Tenant shall not undertake any work in the rented premises that might change
the intended use of the property, or endanger its structural soundness.
Likewise, it shall not cause the flooring to support a weight or charge greater
than the tolerance thereof, i.e., 250 kg per m(2) subject to being liable for
any damage or accidents and it shall verify the authorized weight thereof with
the architect.

All work involving a change of distribution, demolition, or piercing of walls,
beams, or floors, installation of machinery regardless of the energy source,
shall receive the Landlord's prior written authorization, it being understood
that the outfitting work set forth in Chapter I Art. 8 hereof have already been
authorized by the Landlord. To obtain such approval, the Tenant shall provide
the Landlord with a technical file containing all documents relating to the
proposed work or installations and, at a minimum, the plans and technical
description thereof and the tentative schedule for completion.

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The work shall be performed at the expense, risk and responsibility of the
Tenant, subject to supervision by an architect or technical analysis firm and a
quality control firm approved by the Landlord and the fees and expenses of which
shall be borne by the Tenant. It shall obtain the insurance coverage necessary
for completion of the work. The Tenant shall be personally responsible for any
claims made by occupants of the building, neighbor or third parties, including,
but not limited to, in respect of noise, heat, odor, or vibrations

Notwithstanding, the Landlord hereby reserves the right to request dismantling
and removal of machines or motors that may have been installed, even with its
approval, if their operation becomes the basis of claims that are justified by
tenants or neighbors.

In the absence of specific agreement between the Landlord and the Tenant, all
work, embellishments, improvements, installations, and construction of any kind,
including fixed, mobile, or moveable partitions, and any that may be required by
legislative or regulatory provisions made by the Tenant during this Lease shall
become the Landlord's property upon the Tenant's departure without indemnity and
without prejudice to the Landlord's right to require restoration of the
premises, in whole or in part, to their original state, at the Tenant's expense,
even for work expressly approved by the Landlord, except for such as is hereby
already approved under Article 8 of the Special Terms and Conditions. This
paragraph shall be without prejudice to Chapter I Art.8, and, in particular, the
indemnity that may be paid by the Landlord to the Tenant pursuant to such
provisions.

The Tenant shall not affix any plaque, or sign, or awning, or make any
installation of any kind to the exterior of the building or the interior of the
common areas.

It is hereby stated that the Tenant agrees to comply with the graphic chart in
effect for the building's signs, and, in particular, for installation of plaques
on entry doors of the rented premises (see, chart set forth in Exhibit 9
hereof).

3.    OCCUPANCY OF THE PREMISES

The premises, at all times and until expiration or termination of this Lease,
shall contain equipment, furnishings, and merchandises in quantity and value
sufficient to serve as security to the Landlord for payment of rent and all
ancillary obligations under this Lease.

The Tenant shall take out all subscriptions for water, gas, electricity, and
telephone service and pay the premiums and fees connected therewith, so that the
Landlord is not disturbed on account thereof and be responsible for all repairs
that may be necessary to any meters, pipes, as well as taps.

4.    MAINTENANCE AND SURVEILLANCE OF THE PREMISES

The Tenant shall be responsible, at its expense, for making any repairs to the
rented premises during the term of this Lease, even slight repairs, cleaning
and, in general, any restoration or replacements as soon as they become
necessary and regardless of the reason therefor.

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The Tenant, at its expense, shall maintain all specific material and equipment
relating to the private areas, such as air conditioning, ventilation, electrical
and telephone installations in compliance with applicable standards and keep
them in perfect condition for use. For this purpose, it shall enter into any
necessary maintenance agreements and agrees to supply a copy thereof to the
Landlord at its request. The Tenant shall be responsible for maintaining locks,
shutters, closing panels in a condition of complete cleanliness, maintenance,
and operation. Likewise, it shall be responsible for repainting and repairing,
if necessary, and maintaining the mirrors and windows, floors, tiles, and
woodwork.

Finally, it shall maintain the coverings of the floors and walls in perfect
condition and, among other things, shall remove and repair any stains, burn
marks, tears, holes, or detachments. If such maintenance work is not performed,
the Landlord shall have the right to have it performed in the Tenant's place,
after ordering it to be done, by a contractor of its choice, at the Tenant's
exclusive expense, without prejudice to any expenses for restoration that may
result from such damage caused by failure to comply with the provisions of this
clause.

These provisions shall also apply to any expenses that may be applicable in this
respect to the Landlord under the Schedule of Specifications, or any other
document.

The Tenant shall allow the Landlord, its representative, or its architect, and
other contractors and workers to have access to the rented premises and visit
them to inspect the state thereof, any time and as often as may appear useful to
them, during normal business hours, except for in cases of emergency. It shall
also allow access to the premises to workers that may have to perform work that
may be deemed useful or necessary. The Landlord, in any event, shall give the
Tenant prior notice of at least two (2) business days in advance and shall cause
such visits and/or workers accessing the premises to be the least disruptive as
possible to its operations.

The Tenant, in any case, shall do nothing, or allow anything to be done, that
might cause deterioration to the premises, and it shall immediately notify the
Landlord of any injury or damage that might occur to the cleanliness, of any
deterioration or degradation that may occur to the rented premises and of which
it may become aware.

The Landlord shall not be liable, in any event, or in any respect, for theft,
misuse, or disturbance of the area which may occur to the Tenant in the rented
premises, unless such disturbance results from the actions of persons for which
the Landlord is civilly liable, with the Tenant being personally responsible for
ensuring, as it deemed appropriate, the security and surveillance of the rented
premises.

4BIS. REMOVAL OF WASTE OTHER THAN IN THE NORMAL COURSE

The Tenant, at its expense, shall do whatever may be necessary to ensure the
sorting, storage, and removal of waste connected with its operations. The
following are involved, in accordance with the classification of waste contained
in Decree n(degree) 2002-540 date 18 April 2002:

      -     packaging waste: cartons, plastic material, wooden pallets, etc.

      -     ordinary industrial waste: glass, iron, plastic material, cartons,
            plaster, etc.

special industrial waste: paint, oils and lubricants, solvents, sanitary
products, and others. Such products shall mandatorily be stored in a dedicated
building by the Tenant in a special location located outside the building.

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5.    VISIT DURING THE PRIOR NOTICE PERIOD

The Tenant shall allow the Landlord to visit the premises, or cause the premises
to be visited by any person authorized by Landlord, or possible tenants, in the
event this Lease is terminated, during the prior notice period and during normal
business hours, on the condition that the Tenant be advised thereof at least two
(2) business days in advance thereof. It will agree to allow signs to be posted
at places chosen by the Landlord.

6.    CONTRIBUTIONS - TAXES - LEVIES

The Tenant agrees to pay its personal contribution, business tax, rental taxes,
and others of any and all kinds applicable to it specifically or relating to its
business, to which tenants are, or may become, subject, and to pay the tax for
garbage and waste removal, street cleaning tax, all new municipal taxes and
contributions and others, and tax increases that may be enacted and for which
tenants may be responsible of any kind and however called; it shall also bear
the cost of the real estate tax (impot foncier), or any new tax on improved or
unimproved real estate that may be substituted therefor, such that the rent
herein provided shall be net of any charge for the Landlord, as it provided in
Article VI-20(degrees) hereinafter.

7.    INSURANCE AND CLAIMS

      1.    The LANDLORD agrees obtain insurance coverage from insurance
            companies known to be solvent and chosen by it, as follows:

      a -   THE BUILDING FOR ITS VALUE AS NEW including all fittings and
            installations deemed to be fixtures under Article 525 of the Civil
            Code.

            Against any normal risks of destruction and including, but not
            limited to, the following:

            FIRE AND LIGHTENING, EXPLOSIONS, ELECTRICAL DAMAGE, FALLING AIRCRAFT
            AND AIRBORNE OBJECTS, DAMAGE FROM LAND VEHICLES BELONGING TO THIRD
            PARTIES, HURRICANES, CYCLONES, TORNADOES, STORMS, HAIL, SMOKE,
            STRIKES AND CIVIL UNREST, ACTS OF VANDALISM AND MALICIOUS MISCHIEF,
            WATER DAMAGE, ICING.

            The insurance shall include all the coverage annexed hereto,
            especially the loss of rent, clean-up expenses, and experts' fees.

      b -   ITS CIVIL LIABILITY for personal injury or property damage caused
            to third parties as a result of the buildings, installations, and
            outfitting of common areas. It is hereby stated that tenants shall
            be deemed to be third parties as regards each other and vis-a-vis
            the LANDLORD.

      2.    THE LANDLORD HEREBY WAIVES, AND SHALL CAUSE its INSURERS to waive,
            in the event of an event covered by the coverage set forth in
            paragraph 1 a , ANY CLAIMS they may have against the TENANT.

            The TENANT shall reimburse the LANDLORD, with charges, for its share
            of the premiums connected with the policies taken out under Article
            1, as well as for any additional premiums that may result from
            waiver of claims by the Landlord and its insurers against the Tenant
            upon this Lease taking effect.

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      3.    THE TENANT OBTAIN AND MAINTAIN insurance coverage for any normal
            risks of destruction, including, but not limited to, the following:

            FIRE AND LIGHTENING, EXPLOSIONS, ELECTRICAL DAMAGE, FALLING AIRCRAFT
            AND AIRBORNE OBJECTS, DAMAGE FROM LAND VEHICLES BELONGING TO THIRD
            PARTIES, HURRICANES, CYCLONES, TORNADOES, STORMS, HAIL, SMOKE,
            STRIKES AND CIVIL UNREST, ACTS OF VANDALISM AND MALICIOUS MISCHIEF,
            WATER DAMAGE, ICING

            during the term of this Lease of the premises, all OUTFITTING that
            it may have done to the rented premises, FURNISHINGS, EQUIPMENT,
            MATERIAL, MERCHANDISE, GOODS belonging to it and present therein,
            CLAIMS OF NEIGHBORS AND THIRD PARTIES, AS WELL AS FOR ITS CIVIL
            LIABILITY to third parties, as a result of its operations, with a
            company known to be solvent, PAY exactly the premiums and fees of
            such insurance and provide evidence thereof to the LANDLORD whenever
            so requested by it.

            The Tenant shall insure against the risks, if any, related to
            importation into the rented premises of inflammable or explosive
            material, or material that may endanger the building's safety, and
            use of gas in any form.

      4.    THE TENANT HEREBY WAIVES, IN THE EVENT OF AN EVENT covered by the
            coverage set forth in paragraph 3 hereinabove ANY CLAIMS it may have
            against the LANDLORD, any representative or agent of the LANDLORD or
            their Insurers.

      5.    Likewise, the policy SHALL INCLUDE A WAIVER by the insurance company
            of any claims against the LANDLORD of the building, any
            representatives or agents of the LANDLORD, or the Insurers of the
            above-described persons, for their portion of the damage for which
            they may be liable for any reason.

      6.    If the TENANT should fail to obtain such insurance policies and pay
            the premiums therefor, the LANDLORD reserves the right to do so, in
            which case, the TENANT agrees to reimburse it for any amounts paid
            by it in this respect, increased as a matter of right (de plein
            droit) and without notice (sans mise en demeure) for interest at the
            rate indicated hereafter from the day on which such amounts should
            have been paid by the TENANT.

      7.    IF THE BUSINESS CONDUCTED BY THE TENANT CAUSES, for the LANDLORD,
            for other tenants of the building, or for neighbors, ADDITIONAL
            INSURANCE PREMIUMS, the TENANT shall be required both to indemnify
            the LANDLORD for the amount of any additional premium paid and hold
            it harmless against any claims of other tenants or neighbors.

      8.    Additional Insurance:

            It is expressly agreed that the LANDLORD may at any time during the
            term of this Lease obtain itself, of request the TENANT to obtain,
            additional insurance that may appear necessary to it to complete or
            perfect the coverage set forth hereinabove in the event legislation
            should impose it, or a change in the nature of TENANT's business or
            operations, or the use of the premises should require it.

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8.    ASSIGNMENT OF THIS LEASE

The Tenant shall not be entitled to assign or transfer its rights under this
Lease, and any assignment made in violation of this clause shall be invalid and
grounds for terminating this Agreement, in the Landlord's discretion.

9.    SUBLEASES

The Tenant may not grant subleases, in whole or in part, without the consent of
the Communaute d'Agglomeration de Montpellier and the express written consent of
the Landlord.

In any event, in case of authorized sublease, the Landlord shall be given the
opportunity to countersign the document, and the Tenant shall remain solely
liable for all rent to the Landlord and solely liable for the performance of the
charges and conditions of this Lease, with any Sublease being valid only in
connection with the right held by the Tenant hereunder. It is pointed out that
the premises form an indivisible whole and, accordingly, a subtenant shall have
no right either to remain in the premises, or to renewal thereof. It follows
that any sublease shall be made at the Tenant's risks and responsibility, and
the Tenant agrees to be personally responsible for evicting any subtenant.

10.   TELEPHONE

The Tenant shall be personally responsible for obtaining telephone service and
the installation of telephone equipment and, accordingly, shall remain owner of
its lines.

11.   SURRENDER OF THE PREMISES

Before vacating, the Tenant, prior to any removal, even partial, of any
furniture or equipment, shall have paid all installments of rend and ancillary
amounts and have produced evidence in the form of receipts of the payment of
contributions for which it is responsible, both for past years and for the
current year.

The Tenant, no later than the day on which this Lease expires, shall surrender
the rented premises in a good state of repair and maintenance, for which the
Tenant shall be responsible, except for deterioration found to exist in the
state of the premises at the time possession was taken thereof, as set forth in
the last paragraph of this Article 11, which will be determined by an inspection
and report (etat des lieux) following which the Tenant shall surrender the keys
to the Landlord. Such inspection and report, the date of which shall be
determined by mutual agreement of the parties, shall include, if necessary, a
list of repairs to be made.

Despite surrendering the keys, this Lease shall continue until expiration
thereof, with rent remaining due until the end of its term. Otherwise, the
inspection and report thereof shall be prepared on the date this Lease expires.

If the Tenant should not be present on the date and at the time set for the
inspection and report, it shall be prepared at the Landlord's discretion in the
presence of a court bailiff (huissier), which may be assisted by a locksmith to
gain entry into the premises, with the related expenses to be at the Tenant's
exclusive responsibility.

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If repairs or work is necessary, the Tenant, within fifteen days from
notification of estimates prepared at the Landlord's request, shall indicate its
agreement to such estimates. If the Tenant does not indicate its intentions
within the above-described time period, the estimates shall be deemed approved,
and the Landlord shall be entitled to have the work performed by the contractors
of its choice, claiming the amount from the Tenant.

If the Tenant indicates its intentions to perform the work itself, it shall
commit to have it performed, as an essential and determining condition, promptly
by qualified contractors approved by the Landlord, the consent of which shall
not be unreasonably withheld.

During the pendency of the restoration work, following the end of this Lease,
given the unavailability of the premises, an occupation indemnity equivalent to
the rent and charges shall be due by the Tenant.

Repairs shall include restoration of the premises, as determined during the
inspection and report prepared after completion of the outfitting work set forth
in Chapter I Art.7.

12.   CHANGES IN THE ARTICLES OF ASSOCIATION OF THE TENANT AND INFORMATION TO
      THE LANDLORD

During the term of this Agreement, in the event of any change in the Articles of
Association of the Tenant (transformation, change in company name or purposes,
change of Managing Director, etc.) and given the personal quality of the
contractual relationship, ("intuitus personae"), the Tenant shall notify the
Landlord, during the months preceding the occurrence thereof, of any change to
be made and shall obtain the Landlord's prior consent, after advising the
Communaute d'Agglomeration de Montpellier, subject to this Agreement being
terminated, in the Landlord's discretion.

The Landlord and the Communaute d'Agglomeration de Montpellier hereby reserve
the right at any time to demand copies of the balance sheet and income statement
of the business conducted in the rented premises.

ARTICLE VI- FINANCIAL OBLIGATIONS

1.    RENT

THE RENT ESTABLISHED in the special terms and conditions constitute an essential
and determining clause for the two parties to the making of this Lease. This
Lease is granted and accepted in consideration of an annual base rent, the
amount of which is set forth in Chapter I Art. 6 and which is subject to change
on the terms and conditions prescribed by law and on the basis of the terms and
conditions set forth in Article VI-60 hereafter.

2.    ANCILLARY EXPENSES TO THE RENT

a) The Tenant shall reimburse the Landlord, at the time it pays each installment
of rent, for its portion of individual services and furnishings, including
expenses for heating, insuring the building, taxes presently applicable and
those that may become applicable, expenses for managing the building, fees of
the managing agent, condominium charges, if the building is in that form, or of
any other company of which the building may be a part, and, in general, all
operating, repair (except major repairs within the meaning of Article 606 of the
Civil Code), and maintenance expenses applicable to the premises and equipment
and furnishings of any kind, both of the rented premises and the areas deemed
common to the building, so that the rent herein provided

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shall be net of any charges for the Landlord.

b) The division of charges among the various tenants shall be in proportion to
the weighted average of areas of the premises rented, or to be rented, in the
building.

Such reimbursement shall be made by call of a quarterly reserve to be paid by
the Tenant with each installment of rent. To take account of variations in the
charges, the Landlord, upon providing supporting documentation therefor, may
change the amount of the reserve for charges.

At the end of each annual period, the amount of the reserve paid shall be
settled on the basis of an accounting of the annual charges, and the Landlord
shall provide the Tenant with all books and records supporting such payments.

3.    TAXES AND FEES

Since the Landlord has elected to subject the rent to VAT, under Article
260-2(degree) of the French Tax Code, the above-indicated rent and the ancillary
charges thereto shall be increased by TVA at the rate applicable at the time of
invoicing.

The Landlord reserves the right to cease applying VAT to this Lease, in its
discretion. In such case, the rent shall be subject to any other fee or tax that
may replace it or be substituted therefor, which will be borne by the Tenant.

4.    TERMS AND CONDITIONS OF PAYMENT

The Tenant hereby agrees to pay to the Landlord the rent and amounts ancillary
thereto in four equal installments in advance on the first of January, April,
July, and October of each year.

All payments shall be made at the Landlord's domicile, or any other place
indicated by it.

In case of non-payment when due of the rent due by the Tenant, or any other
amount due under this Lease that is not paid by the applicable deadline, the
Landlord, as a matter of right (de plein droit) and 30 days after prior notice
thereof that remains uncured, shall receive interest of 1% per month of delay,
calculated as from the due date of the claim, with such increase providing
grounds for delaying payment. Any month begun shall be counted as a whole month.

In addition, in the event of more than one breach by the Tenant and upon
expiration of 15 days from the due dates involved, all amounts due and payable
shall be increased as a matter of right (de plein droit) by a fixed 10% as a
penalty, without any requirement of notice and warning (mise en demeure) and
without prejudice to application of the rescission clause.

Late payment of two notices of amounts due and owing, whether or not
consecutive, shall constitute a serious and legitimate ground for rescinding
this Lease.

5.    SECURITY DEPOSIT

To secure performance of the obligations for which it is responsible, the Tenant
shall pay to the Landlord, which acknowledges receipt thereof, an amount
representing three months' rent (excluding taxes) as a security deposit. Such
deposit shall not bear interest, nor be deductible from the last installment of
rent and shall be refundable after the Tenant's departure, subject, on the one
hand, to payment of all amounts due by the Tenant and especially the balance of
charges relating to its period of occupancy, and, on the other hand, payment of
expenses for restoring the

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premises rented.

In the event of revision or variation in the amount of the rent hereinabove
provided, this deposit shall be adjusted in proportion to the new rent and on
the same terms and conditions.

In the event of termination of this Lease, as a result of breach of such
conditions for any reason attributable to the Tenant, such deposit shall be
vested in the Landlord as initial damages, without prejudice to any other.

Upon the Tenant's departure, the security deposit shall be applied on a priority
basis against the amount of repairs due by the Tenant, as set forth in Article
V-11(degrees).

The Tenant hereby expressly waives receipt of interest on such security deposit.

6.    INDEXATION CLAUSE

The rent shall also be subject to the following indexation clause: it shall vary
automatically every year in proportion to the variations in the quarterly index
of the cost of construction published by the Institut National de la Statistique
et des Etudes Economiques (French National Institute for Statistics and Economic
Studies). For the first year, the index as set forth in Chapter I Art. 10 and
shall be compared to the index for the same quarter of the following year.

For subsequent years, the comparison shall be with indices used for the previous
revaluation, and the index for the same quarter of the subsequent year.

If such index is not known on the anniversary date of this Lease, a provisional
indexation shall be made on the basis of the last known index.

If, for any reason, the above-described index used for annual revision of rent
should no longer be published, such revision shall be made by taking as a basis
either the successor index, or a new index mutually agreed.

If agreement cannot be reached on the choice of a new index to be used, the
parties hereby agree to accept the decision of an expert appointed by the
Presiding Judge of the Tribunal de Grande Instance (High Court of Justice) of
the place where the building is located.

ARTICLE VII - OTHER OBLIGATIONS

1.    TOLERANCES

It is formally agreed that any tolerances on the part of the Landlord relating
to clauses and terms and conditions of this Lease, regardless of their frequency
or duration, shall in no event be deemed to constitute amendments to, or waivers
of, such conditions, nor the source of any right of any kind. The Landlord shall
always have the right to end them.

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2.    RESCISSION CLAUSE

It is expressly agreed that, failure by the Tenant to perform any of the
obligations and terms and conditions of this Lease shall constitute a serious
and legitimate ground for rescission, or, that in the event of failure to make
due and punctual payment of any installment of rent and ancillary expenses, or
an arrears of rent resulting from a revision at the due date thereof, this
Lease, at the Landlord's discretion may be rescinded as a matter of right (de
plein droit) and without any legal or court formality, one month after simple
notice to perform, or a simple order to pay served in person, or at domicile,
containing a statement by the Landlord of its intention to avail itself of this
clause, that remains uncured during such period.

3.    OCCUPATION OF THE PREMISES AFTER TERMINATION OR RESCISSION OF THIS LEASE

If, after termination or rescission of this Lease, the premises are not
surrendered to the Landlord on the agreed date, free of all occupancy, the
occupancy indemnity due by the Tenant and persons claiming from, through, or
under it until restitution and due and payable each day that passes, shall be
equal to the last rent, plus 50%. The charges shall also be due up to the day
when the premises have been surrendered to the Landlord, without prejudice to
any other damages, except as otherwise specifically agreed by the parties.

4.    COSTS

All costs and expenses of any documents, stamp or registration duties, if any,
as well as those that may be the consequence the result or consequence thereof,
including, but not limited to, any reasonable expenses incurred by the Landlord
(fees of attorneys, court bailiffs, etc.) as the result of any actions validly
taken against the Tenant to obtain performance of the clauses and terms and
conditions of this Agreement, shall be borne by the Tenant, which hereby
expressly agrees thereto.

In addition, the Tenant shall pay an indemnity fixed at 20% of the amounts with
respect to which proceedings may be commended, which indemnity shall be used to
cover the Landlord's damages resulting from the delay in payments. It shall be
considered as additional and accessory to the rent. Accordingly, it shall be
paid at the same time as the amounts due under this Lease.

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5.    ELECTION OF DOMICILE

For purposes hereof, domicile is hereby elected, for the Landlord, at its
registered office, for the Tenant in the rented premises.

      Made in Montpellier, on April the 18th 2005.

      In three originals.

                 THE LANDLORD                                 THE TENANT
           MR. ANDRE LE GRAVEREND                    MR. JEAN-PIERRE SOMMADOSSI
                                                     GERANT
     (handwritten legend "lu et approuve "  (handwritten legend "lu et approuve"
           "accepted and agreed"                  "accepted and agreed"
               Company seal)                         Company seal)

                                  THE INTERVENOR
                               Mr. Georges FRECHE,
                     President of Communaute d'Agglomeration
                                  de Montpellier

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                                                                    EXHIBIT 10.2

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

                                  OFFER OF SALE
                          HOTEL D'ENTREPRISES CAP GAMMA

BETWEEN

SOCIETE D'EQUIPEMENT DE LA REGION MONTPELLIERAINE, "SERM", a French public
sector "mixed economy" corporation (societe anonyme d'economie mixte), the
registered capital of which is EUR 5,894,000, the registered office of which is
located in Montpellier (34000), Hotel de Ville, identified with the SIREN under
number 462800160 and registered with the Registry of Commerce and Companies
(Registre du Commerce et des Societes) of Montpellier,

Herein represented by its General Manager (Directeur General), Mr. Eric BERARD
under authority granted to him by SERM's Board of Directors at a Meeting held on
2 October 2002,

Hereinafter called "SERM"

                                                                On the one hand,

AND

IDENIX SARL, a French limited liability company (societe a responsabilite
limitee), the registered capital of which is EUR 1,000,000, the registered
office of which is located in Montpellier, 170, rue Leon Blum, 34000, and which
is registered with the Registry of Commerce and Companies (Registre du Commerce
et des Societes) of Montpellier under number 419 909 148,
herein represented by Mr. Jean-Marc ALLAIRE, Vice President for Europe
(Vice-President, Direction Europe), under a power-of-attorney granted to him and
dated 6 November 2000 by Mr. Jean-Pierre SOMMADOSSI, Managing Director (Gerant)
of SARL IDENIX,

Hereinafter called "IDENIX"

                                                              On the other hand,

SERM and IDENIX are hereinafter separately called a "PARTY" and together the
"PARTIES".

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RECITALS:

SERM owns a real estate complex called CAP GAMMA, intended to house companies
that specialize in biotechnology and pharmaceutical chemicals located in the
development zone called ZAC EUROMEDECINE II in the Town of Grabels, rue de la
Valsiere.

Such real estate complex was built by SERM at the request of the Metropolitan
Area (Communaute d'Agglomeration) of Montpellier, following Amendment n(degree)1
to the Public Development Agreement (Convention Publique d'Amenagement), dated
30 July 2002.

Under the Public Development Agreement, development of the zone is undertaken by
SERM under the supervision of the Metropolitan Area (Communaute d'Agglomeration)
at its financial risk.

Upon the expiration of the Pubic Development Agreement, this real estate
complex, or the portion thereof that has not been rented, will revert to the
Montpellier Metropolitan Area (Communaute d'Agglomeration de Montpellier), which
will then be required to assume future responsibility for performance of the
agreements binding it to third parties.

On 15 December 2004, the Parties entered into a Bilateral Offer to Lease
(Promesse Synallagmatique de Bail) under which SERM offered to rent to IDENIX,
for a term of twelve years as from 15 April 2005, the space that will gradually
be made available to IDENIX on basis, pursuant to a schedule agreed by the
Parties.

Thus, as from 1st April 2007, IDENIX will occupy space having total usable area,
after preparation of the private portion, of 3,271.60 m(2) and will have 56
outside parking places in the area of A Building, as well as 24 outside parking
places that will be made available to the Tenant upon completion of the 2nd
phase of the CAP GAMMA program (B Building).

Under the Offer to Lease hereinabove described, IDENIX has agreed to use the
above-described space for offices and laboratories for the purpose of engaging
in any operations and activities relating to pharmaceutical research, scientific
research, the manufacture, marketing, and sale of pharmaceutical products.

Given the investments that will be made by IDENIX in the space covered by the
Offer to Lease, IDENIX has advised SERM of its strong interest in being able to
acquire such space.

SERM has advised IDENIX that it is willing to agree to sell the space to IDENIX,
if it advises its intention to make the acquisition thereof on the terms and
conditions hereinafter set forth.

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NOW, THEREFORE, THE PARTIES HERETO HEREBY AGREE AS FOLLOWS:

ARTICLE 1ER - PURPOSE

SERM hereby grants to IDENIX the right to acquire, if it so wishes, on the terms
and conditions hereinafter set forth, the real estate assets leased by IDENIX on
the terms and conditions set forth in the Lease Agreement to be made between the
Parties and the Communaute d'Agglomeration as provided in the Offer to Lease
(Promesse Synallagmatique) described in the Recitals hereto (hereinafter called
the "LEASE AGREEMENT") and more fully described in such Offer to Lease (Promesse
Synallagmatique de Bail) with which IDENIX represents and warrants that it is
quite familiar as a result of having seen and visited them for the purposes
hereof and the Bilateral Offer to Lease (Promesse Synallagmatique de Bail) (such
real estate assets being hereinafter called the "REAL ESTATE COMPLEX").

ARTICLE 2 - CONDITION PRECEDENT

This Offer of Sale is subject to the condition precedent of obtaining via a
resolution adopted by the Communaute d'Agglomeration of Montpellier, or any
other action taken by the Communaute d'Agglomeration of Montpellier authority
for SERM to sell the Real Estate Complex located in the area covered by the
Convention Publique d'Amenagement (Public Development Agreement).

If the foregoing condition precedent is not met, this Offer of Sale shall be
deemed to be null and void, and no indemnity shall be due by either party to the
other.

ARTICLE 3 - TERMS AND CONDITIONS OF THE OFFER

3.1      SERM's Covenant

SERM hereby agrees to sell the Real Estate Complex described in Article 1 above
to IDENIX on the terms and subject to the conditions hereinafter set forth.

3.2      Negative Covenants of SERM

During the term of this Offer of Sale, SERM agrees not to grant any rights or
options, real or personal, nor any charge or lien in or against the Real Estate
Complex, or to alienate or transfer such Real Estate Complex to any person other
than IDENIX or the Communaute d'Agglomeration of Montpellier.

3.3      IDENIX's Rights

IDENIX accepts this Offer of Sale as an option, but reserves the right to seek
or forego completion thereof, in its discretion.

3.4      Request to Complete

IDENIX may request completion of the sale either by service of a notice to that
effect by a court bailiff (exploit d'huissier), or by registered letter, return
receipt requested, or by a letter personally delivered, against receipt
therefor, to SERM.

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Regardless of the method used, the desire to make the acquisition shall reach
SERM no later than during the day on which the periods set forth hereinafter
expire, under penalty of forfeiture:

      3.4.1 Purchase Upon Expiration of the Lease Agreement:

      IDENIX shall advise SERM no later than twelve (12) months prior to the
      expiration date of the Lease Agreement of its decision whether or not to
      acquire the Real Estate Complex.

      After such deadline, and solely as a result of expiration of such term
      IDENIX, as a matter of right (de plein droit) and without formal notice
      (mise en demeure) shall forfeit the right to request completion of the
      sale.

      3.4.2 Early Purchase:

      As an express exception to Article 3.4.1 hereof, IDENIX shall have the
      right to acquire the Real Estate Complex earlier by giving notice to SERM
      of its decision to acquire at least twelve (12) months prior to the
      proposed date thereof and only as from six (6) years after the effective
      date of the Lease Agreement.

3.5 Finalization by Authenticated Deed:

The sale, if it is completed, shall take place by a deed authenticated and
notarized by Maitre DOMERGUE, Notary of the ZAC EUROMEDECINE II zone, to whom
IDENIX's Notary shall lend his/her assistance.

3.6 Terms and Conditions of a Possible Sale:

The sale, if it is completed, shall occur on the basis of charges and conditions
that are ordinary and customary in such matters, including, but not limited to,
for the buyer, taking the assets sold "as is" in the state in which they exist
and of which they consist, on the date of sale.

The Sale, furthermore, shall be subject to the express condition that:

      -     the business conducted by IDENIX SARL be substantially the one
            conducted on the date the Promesse synallagmatique de bail
            (Bilateral Offer of Lease) and Administrative Lease (Bail
            administrative) are made;

      -     IDENIX SARL have met all its obligations under the Lease Agreement,
            including, but not limited to, payment of all rent and charges due
            and owing under the Lease.

ARTICLE 4 - OWNERSHIP - POSSESSION

4.1      Purchase Upon Expiration of the Lease Agreement:

By express agreement of the Parties and to ensure the uninterrupted possession
of the real estate complex by IDENIX, if the sale occurs, the Parties agree to
accomplish the formalities of signing the authenticated notarized deed so that
IDENIX shall be the owner on the date the Lease Agreement terminates.

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4.2      Early Purchase:

By express agreement of the Parties, if the sale is completed early, as set
forth in Article 3.4.2 hereof, IDENIX shall become the owner of the Real Estate
Complex as from signature of the authenticated notarized deed. The completion of
the sale by authenticated notarized deed shall occur no later than expiration of
the twelve (12) month period set forth in Article 3.4.2.

4.3      Failure to Complete by Deadlines:

If completion by authenticated notarized deed does not occur, a statement of
such failure shall be prepared at the request of the party acting first, which
will then have the right to seek relief in the courts to obtain completion of
such sale, or rescission of this Offer, the consequences to be borne by the
defaulting Party.

If the sale is completed as a result of a court order, entry of possession shall
occur on the date of such order.

ARTICLE 5 - PRICE

5.1      Acquisition Upon Expiration of the Lease Agreement:

The price of the sale of the Real Estate Complex that occurs upon expiration of
the Lease Agreement, as provided in Article 3.4.1 hereof, is hereby fixed at
[**] EUROS (E [**]). It shall be increased by an amount equal to any rent,
ancillary costs, and interest (interets moratoires) that may be due under the
Lease Agreement and that may not have been paid on the date on which payment is
due to be made.

It shall be increased, furthermore, by the amount of VAT that should be paid by
SERM to the Public Treasury under Article 210, Annex II of the French Tax Code.
SERM shall prepare a certificate attesting to payment of the VAT by it, so as to
enable IDENIX to recover such VAT.

All fees, taxes, and charges relating to such transfer, including under any
condominium by-laws or regulations, shall be borne exclusively by IDENIX, which
hereby agrees thereto.

5.2      Premature Purchase:

If the sale should be completed earlier, as provided in Article 3.4.2 hereof,
the sale price is hereby fixed at:

      -     EUR [**] for an acquisition between the ninth and twelfth years.

      -     EUR [**] for an acquisition in the eighth year.

      -     EUR [**] for an acquisition in the seventh year.

      -     EUR [**] for an acquisition in the sixth year

increased by the amount of VAT that should be paid by SERM to the Public
Treasury (Tresor) under Article 210, Annex II, of the French Tax Code, and the
amount of the fees and expenses of the transfer. In addition, SERM shall prepare
a certificate attesting to payment of the VAT by it, so as to enable IDENIX to
recover such VAT.

Such price shall be due and payable in full upon signature of the authenticated
notarized deed, without any option for the buyer to pay the amount due in
installments.

INITIALS:
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TRANSLATION FROM FRENCH-FOR INFORMATION ONLY                                   6

ARTICLE 6 - RECORDING

Recording hereof is required for a fixed fee under Article 680 of the French Tax
Code. SERM will undertake the recording formalities within 10 days, at the
Beneficiary's exclusive cost.

ARTICLE 7 - DOMICILE

For purposes hereof, the Parties elect domicile as follows: SERM at its
registered office, and IDENIX in the premises covered by the Lease Agreement.

Made in Montpellier,
On 17 December 2004
In three originals

For SERM                                       For IDENIX
Mr. Eric Berard                                Mr. Jean-Marc ALLAIRE

/s/  Eric Berard                               /s/ Jean-Marc ALLAIRE
-----------------------                        ----------------------------
Director General de la SERM                    Jean-Marc ALLAIRE representing
                                               Jean-Pierre Sommadossi for Idenix

INITIALS:

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