PRAECIS PHARMACEUTICALS INCORPORATED Announces Pilot Study and Option Agreement with GlaxoSmithKline to Utilize DirectSelect(TM

PRAECIS PHARMACEUTICALS INCORPORATED (NASDAQ: PRCS)
today announced that it has entered into a two year pilot study and
option agreement with GlaxoSmithKline, a leading global pharmaceutical
company (GSK), through its recently established Center of Excellence
for External Drug Discovery (CEEDD). The goal of this pilot study is
to apply PRAECIS' DirectSelect(TM) technology to identify small
molecule lead drug candidates against a diverse set of four targets
selected by GSK. The pilot study is consistent with the mission of
GSK's CEEDD to leverage the potential of innovative drug discovery
technologies to identify novel therapeutic candidates for GSK's global
research and development organization.

   Under the terms of the agreement, following identification by
PRAECIS of lead compounds meeting pre-established success criteria
against at least one of the specified targets, GSK will have the
exclusive option to enter into a broader strategic alliance for
further discovery and development of such lead compounds. The pilot
agreement contemplates that any broader strategic alliance could cover
one or more of the targets included in the pilot study, as well as
additional targets as may be agreed upon by the parties.

   Maxine Gowen, Ph.D., Senior Vice President of GSK and head of the
Center of Excellence for External Drug Discovery at GSK stated, "In
developing this drug discovery technology, PRAECIS has overcome
multiple challenges in creating and screening large libraries of
molecules. We look forward to exploring with PRAECIS the breadth of
impact that this technology could have on discovering lead molecules
against both standard and more challenging targets of interest to
GSK."

   Kevin McLaughlin, President and Chief Executive Officer of PRAECIS
stated, "We are extremely pleased to announce that we are
collaborating with GSK on drug discovery and believe that the CEEDD is
uniquely positioned to investigate with us the potential of
DirectSelect(TM) to rapidly identify novel compounds for drug
development. We view this as a tremendous opportunity to demonstrate
the utility of DirectSelect(TM) in a well-defined pilot program and
believe that positive results will lead to a broader alliance with
GSK, which would include financial terms representative of the value
created in the pilot study."
 
   In connection with the pilot study agreement, GSK will purchase
$500,000 of PRAECIS' common stock, at a price equal to the average
closing price over a 45-day period ending April 25, 2006. In addition,
during the pilot study, PRAECIS will be entitled to receive a $500,000
milestone payment with respect to each of the first two targets for
which lead compounds are identified meeting the pre-established
success criteria.

   About DirectSelect(TM) Technology

   PRAECIS has developed a chemistry-driven technology, called
DirectSelect(TM), which it believes will facilitate the drug discovery
process. The technology is based upon the creation of multiple,
numerically large (10 to the seventh to >10 to the ninth), encoded
libraries of drug-like structures that can be rapidly screened to
identify individual structures, or families of structures, with
affinity for a macromolecular target.

   The premise behind the DirectSelect(TM) technology is that the
odds of identifying hits with higher affinity and enhanced selectivity
for a macromolecular target can be improved by increasing the numeric
size and "chemical space" interrogated by the target. In addition,
access to multiple, structurally diverse families should improve the
likelihood of identifying a lead molecule with a favorable safety
profile in vivo. Combinatorial libraries of small molecules have
traditionally been constrained to relatively low numbers (up to tens
of thousands) of constituents due to technical limitations associated
largely with deconvolution. PRAECIS has systematically addressed these
challenges by focusing its efforts on marrying validated chemistry
methods with unique screening and deconvolution steps.

   The chemistry approach adopted by PRAECIS is to create libraries
that are both rich in numbers of compounds and structural diversity.
The construction of PRAECIS' libraries is based on a two to four cycle
synthesis utilizing scalable aqueous-based chemistry on an automated
platform. PRAECIS has blended the rules for oral availability
developed by Lipinski (Advanced Drug Delivery Reviews 23, 3-25, 1997)
and Veber (J. Med. Chemistry 45, 2615-2623, 2002) and others into the
design of its libraries for the identification and generation of
pharmaceutically relevant compounds. PRAECIS has succeeded in
constructing multiple libraries that currently aggregate to greater
than five billion compounds. PRAECIS' vision is to continue the
diversification of its library through the addition of new scaffolds
and building blocks.

   PRAECIS intends to continue to develop and enhance its
DirectSelect(TM) technology, enter into pharmaceutical partnerships
for drug discovery and development utilizing this technology, and
utilize the technology to expand its own proprietary development
pipeline.

   About The CEEDD

   GlaxoSmithKline is enhancing the way it discovers and develops
drugs by creating a small dedicated team who will feed the GSK
pipeline solely through the efforts of its external alliances. The
CEEDD (Center of Excellence for External Drug Discovery) was formed as
further validation of GSK's strategy to create small, independent and
accountable R&D teams (Centers of Excellence for Drug Discovery or
CEDDs). In essence, the CEEDD will 'virtualize' a portion of the GSK
pipeline; namely, from Target to Clinical PoC, by forming multiple
risk-sharing/reward-sharing alliances. Capitalizing on the speed and
efficiency of its collaborators will allow GSK to deliver
pharmaceuticals products faster to patients.

   About PRAECIS

   PRAECIS PHARMACEUTICALS INCORPORATED is a biopharmaceutical
company focused on the discovery and development of novel compounds
that have the potential to address unmet medical needs or improve
existing therapies. PRAECIS has a novel MetAP-2 inhibitor, PPI-2458,
in clinical development for cancer indications, including
non-Hodgkin's lymphoma and solid tumors, as well as an innovative drug
discovery technology, DirectSelect(TM), which enables the generation
and practical use of ultra-large libraries for the discovery of orally
active compounds for drug development. PRAECIS has received approval
to market Plenaxis(R) in both the United States and Germany.

   This news release contains forward-looking statements, including
statements regarding the terms of the Company's pilot study and option
agreement with GSK, including potential milestone payments under such
agreement and the possibility of entering into a broader alliance, as
well as the Company's plans for seeking additional partnerships
relating to, and its internal use of, its DirectSelect(TM) technology.
These statements are based on the Company's current beliefs and
expectations as to future outcomes and are not guarantees of future
events or performance. These statements are subject to numerous risks,
uncertainties and assumptions that could cause actual events and
results to differ from those anticipated or projected, including, but
not limited to, the Company's ability to successfully perform under
its agreement with GSK, and if successful, to enter into a broader
alliance with GSK for drug discovery and development, and to continue
development of and enter into additional partnerships relating to its
DirectSelect(TM) technology, as well as the risks set forth from time
to time in the Company's filings with the Securities and Exchange
Commission, including but not limited to the various risks discussed
in the Company's Annual Report on Form 10-K for the year ended
December 31, 2005. The Company undertakes no obligation to update any
forward-looking statement made in this press release to reflect new
information, events or circumstances after the date of this release.