Mail Stop 6010

								August 26, 2005


Jean-Pierre Sommadossi, Ph.D.
Chairman and Chief Executive Officer
Idenix Pharmaceuticals, Inc.
60 Hampshire Street
Cambridge, Massachusetts 02139

	Re:	Idenix Pharmaceuticals, Inc.
		Registration Statement on Form S-3
		Filed August 19, 2005
		File No. 333-127710

Dear Dr. Sommadossi:

	We have limited our review of your filing to those issues we
have
addressed in our comments.  Where indicated, we think you should
revise your document in response to these comments.  If you
disagree,
we will consider your explanation as to why our comment is
inapplicable or a revision is unnecessary.  Please be as detailed
as
necessary in your explanation.  In some of our comments, we may
ask
you to provide us with information so we may better understand
your
disclosure.  After reviewing this information, we may raise
additional
comments.

	Please understand that the purpose of our review process is
to
assist you in your compliance with the applicable disclosure
requirements and to enhance the overall disclosure in your filing.
We
look forward to working with you in these respects.  We welcome
any
questions you may have about our comments or any other aspect of
our
review.  Feel free to call us at the telephone numbers listed at
the
end of this letter.

General

1. It appears you were not eligible to use Form S-3 at the time
you
filed the registration statement.  General Instruction I.A.3(b)
requires the timely filing of "all reports required to be filed
during
the twelve calendar months and any portion of a month immediately
preceding the filing of the registration statement" (emphasis
added).
Your Form 10-Q for the quarter ended June 30, 2004 was required to
be
filed by August 16, 2004.  However, it was not filed until August
26,
2005.  Therefore, it appears you are ineligible to file on Form S-
3
until September 1, 2005.  Please either file a pre-effective
amendment
on Form S-1, or withdraw the Form S-3 and re-file it on or after
September 1, 2005.  See Division of Corporation Finance Manual of
Publicly Available Telephone Interpretations (July 1997) G.25,
which
is available at www.sec.gov.

2. We note you have two confidential treatment requests that are
pending.  All comments related to these requests will need to be
resolved prior to effectiveness.

Selling Stockholders, page 6

3. We note the statement on page 7 that the Selling Stockholders
table
"may be expanded or supplemented in prospectus supplements as new
information becomes available to us."  Please be advised that you
may
not use a prospectus supplement to add selling stockholders to the
table unless the new seller is a transferee of a seller who was
identified in the table pre-effectively.  We also note the Selling
Stockholders table currently does not identify any sellers.

* If you do not identify any sellers pre-effectively, you will not
be
able to use a prospectus supplement to update the table after
effectiveness.  Please revise the statement to say the sellers
will be
identified in a post-effective amendment.
* Alternatively, if you identify sellers pre-effectively, you
should
revise the statement to acknowledge the fact that you might use a
post-effective amendment to update the table.

*	*	*

	As appropriate, please amend your registration statement in
response to these comments.  You may wish to provide us with
marked
copies of the amendment to expedite our review.  Please furnish a
cover letter with your amendment that keys your responses to our
comments and provides any requested information.  Detailed cover
letters greatly facilitate our review.  Please understand that we
may
have additional comments after reviewing your amendment and
responses
to our comments.

	We urge all persons who are responsible for the accuracy and
adequacy of the disclosure in the filing to be certain that the
filing
includes all information required under the Securities Act of 1933
and
that they have provided all information investors require for an
informed investment decision.  Since the company and its
management
are in possession of all facts relating to a company`s disclosure,
they are responsible for the accuracy and adequacy of the
disclosures
they have made.

	Notwithstanding our comments, in the event the company
requests
acceleration of the effective date of the pending registration
statement, it should furnish a letter, at the time of such
request,
acknowledging that:

* should the Commission or the staff, acting pursuant to delegated
authority, declare the filing effective, it does not foreclose the
Commission from taking any action with respect to the filing;

* the action of the Commission or the staff, acting pursuant to
delegated authority, in declaring the filing effective, does not
relieve the company from its full responsibility for the adequacy
and
accuracy of the disclosure in the filing; and

* the company may not assert staff comments and the declaration of
effectiveness as a defense in any proceeding initiated by the
Commission or any person under the federal securities laws of the
United States.

	In addition, please be advised that the Division of
Enforcement
has access to all information you provide to the staff of the
Division
of Corporation Finance in connection with our review of your
filing or
in response to our comments on your filing.

	We will consider a written request for acceleration of the
effective date of the registration statement as confirmation of
the
fact that those requesting acceleration are aware of their
respective
responsibilities under the Securities Act of 1933 and the
Securities
Exchange Act of 1934 as they relate to the proposed public
offering of
the securities specified in the above registration statement.  We
will
act on the request and, pursuant to delegated authority, grant
acceleration of the effective date.

	We direct your attention to Rules 460 and 461 regarding
requesting acceleration of a registration statement.  Please allow
adequate time after the filing of any amendment for further review
before submitting a request for acceleration.  Please provide this
request at least two business days in advance of the requested
effective date.

	Please contact Greg Belliston at (202) 551-3861 or me at
(202)
551-3715 with any questions.

								Sincerely,



								Jeffrey P. Riedler
								Assistant Director

cc:	Susan W. Murley, Esq.
	Wilmer Cutler Pickering Hale and Dorr LLP
	60 State Street
	Boston, Massachusetts 02109
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Jean-Pierre Sommadossi, Ph.D.
Idenix Pharmaceuticals, Inc.
August 26, 2005
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