Filed by Genzyme Corporation (Commission File No. 000-14680)
                         pursuant to Rule 425 under the Securities Act of 1933
 Subject Company: GelTex Pharmaceuticals, Inc. (Commission File No. 000-26872)

[GENZYME LOGO]                                                   [GELTEX LOGO]

GENZYME CONTACTS:                                    GELTEX CONTACTS:
- -----------------                                    ----------------
Sally Curley (investors)                             Mark Skaletsky
617-591-7140                                         781-434-3500
                                                     Paul Mellett
                                                     781-434-3484

Bo Piela (media)                                     Lisa Burns (investors)
617-252-7785                                         Justin Jackson (media)
                                                     Burns McClellan Inc.
                                                     212-213-0006

FOR IMMEDIATE RELEASE
September 11, 2000

                GENZYME GENERAL TO ACQUIRE GELTEX PHARMACEUTICALS
                  --------------------------------------------
     SEES RENAGEL(R) AS POTENTIAL BLOCKBUSTER AND IMPORTANT DRIVER OF GROWTH

         CAMBRIDGE and WALTHAM, Mass.--Genzyme General (Nasdaq: GENZ) and GelTex
Pharmaceuticals Inc. (Nasdaq: GELX) today announced that they have entered into
a definitive merger agreement under which Genzyme will acquire GelTex. The
transaction is expected to close in the fourth quarter, pending regulatory and
GelTex shareholder approval.

         With the acquisition, Genzyme General will obtain two patent-protected,
marketed products--Renagel(R) (sevelamer hydrochloride) and WelChol(TM)
(colesevelam hydrochloride)--along with a significant pipeline of promising
products and a proven

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Genzyme General to Acquire GelTex Pharmaceuticals--2

and productive polymer technology platform. Renagel is a rapidly growing product
used in the  treatment  of patients  with  end-stage  renal  disease  undergoing
dialysis.  WelChol is a new  cholesterol-lowering  agent  which will be launched
this month by Sankyo-Parke Davis.

         Genzyme believes that the worldwide market opportunity for Renagel is
far greater than originally anticipated, and believes that Renagel will
transform clinical practice and outcomes. Genzyme expects that at least four
fundamental factors will propel the product's exponential growth: rapidly
increasing market share driven by mounting evidence about the role of calcium in
cardiovascular disease among dialysis patients; appropriate adjustment of daily
doses of Renagel by physicians to lower patient phosphorus levels into the
normal range; substantial growth in the dialysis patient population; and the
potential for Renagel to lower the overall cost of caring for dialysis patients.

         "We have concluded that Renagel has the potential to become a
blockbuster product and that it will serve as an important driver of our future
growth," said Henri A. Termeer, chairman and chief executive officer of Genzyme
Corp. "We believe that Renagel represents the most important advance in the
treatment of dialysis patients since the introduction of Epogen(R). We expect to
soon begin a large clinical trial to study the product's ability to improve
morbidity and mortality. Genzyme expects that the market potential for Renagel
will surpass $500 million within five years and that it will reach $1 billion
within the decade. We have developed a very close relationship

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Genzyme General to Acquire GelTex Pharmaceuticals--3

with the GelTex team through our successful  partnership to bring Renagel to the
market. We value them highly and look forward to a promising future together."

         Mark Skaletsky, president and chief executive officer of GelTex, said:
"Our merger with Genzyme will provide tremendous value to GelTex shareholders
and employees. The combination of Genzyme's resources and global commercial
infrastructure with GelTex's demonstrated ability to develop products, creates a
very powerful company with an outstanding product pipeline. We are very proud of
all that we have accomplished over the last eight years and look forward to
joining with Genzyme to build a significant company that provides therapeutic
products that improve human health."

TERMS OF THE AGREEMENT

         Under the terms of the agreement, GelTex shareholders will receive
0.7272 of a share of Genzyme General common stock or $47.50 in cash for each
GelTex share owned, subject to proration to maintain the cash portion of the
consideration at 50 percent, approximately $500 million. The merger
consideration represents a 27 percent premium over GelTex's closing share price
on September 8, 2000.

         The tax-free transaction has a total value of approximately $1 billion,
based on GelTex's 21.4 million shares outstanding today and Genzyme General's
closing share price of $65.3125 on September 8.

         The boards of directors of Genzyme Corp. and GelTex have approved the
transaction, which is subject to clearance under the Hart-Scott-Rodino
Anti-Trust Improvements Act. The transaction will require the approval of GelTex
shareholders, and is subject to customary closing conditions.

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Genzyme General to Acquire GelTex Pharmaceuticals--4

         Genzyme General expects that the acquisition of GelTex may result in a
one-time charge in the fourth quarter of 2000, related to the write-off of
in-process research and development. The acquisition, which will be accounted
for as a purchase transaction, is expected to be dilutive to Genzyme General's
near-term earnings but is expected to become accretive to earnings in 2002 prior
to depreciation and amortization of good will.

         GelTex employs approximately 110 people. Genzyme plans to retain
GelTex's administrative offices and laboratories in Waltham, Massachusetts. In
addition to its marketed products, its pipeline, and unique polymer technology,
GelTex has assets that include approximately $119 million in cash, usable net
operating loss tax carry forwards, important intellectual property protecting
Renagel and their other products, and research facilities.

RENAGEL'S POTENTIAL FAR GREATER THAN INITIALLY ANTICIPATED

         Renagel's growth will be driven by four key factors: rapidly increasing
market share from its establishment as a preferred first-line treatment, dose
adjustment by nephrologists to lower phosphorus levels into the normal range,
substantial growth in the number of dialysis patients worldwide, and Renagel's
potential to lower the total cost of treating these patients.

         Specifically, Genzyme expects that the fundamental change in clinician
perspectives toward calcium-based binders will rapidly drive the growth of new
prescriptions for Renagel, which is the only calcium-free, aluminum-free
phosphate binder on the market. Currently, the majority of all dialysis patients
are still on a calcium-based phosphate binder.

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Genzyme General to Acquire GelTex Pharmaceuticals--5

         Within the last year, independent clinical evidence showing the
relationship between elevated calcium intake and cardiovascular disease among
dialysis patients has led to questions about the safety of calcium-based
binders. Cardiovascular disease occurs at a markedly higher rate--and is the
leading cause of death--in the dialysis population.

         In response to this new clinical evidence, thought leaders within the
nephrology community have begun to change the way dialysis patients are managed.
According to Dr. Geoffrey A. Block, lead author of the landmark 1998 study
correlating poor phosphorus management with mortality in dialysis patients: "The
changing mindset of nephrologists across this country is based on both research
and personal clinical experience. Too many of our patients die from heart
disease, and now we recognize that our treatment of patients is inadvertently
contributing to the problem. Leading experts on dialysis are recommending much
lower levels of calcium intake. Renagel is the only FDA approved product on the
market that lowers phosphorus without adding calcium. Renagel is therefore
becoming the standard of care and first-line therapy for every single patient on
dialysis."

         To demonstrate Renagel's ability to slow cardiac calcification, Genzyme
is currently conducting a three-year study comparing the product with standard
calcium binders. One-year results will be available during the first half of
2001.

         This study is also designed to further study Renagel's ability to lower
phosphorous into the normal range. Renagel has shown that it can safely lower
serum phosphorous levels into the normal range--a historically difficult
challenge for nephrologists. Many physicians have begun to increase the dosage
level of Renagel in

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Genzyme General to Acquire GelTex Pharmaceuticals--6

their  patients  in order to  achieve  that  goal.  The  launch of a new  tablet
formulation of Renagel this month will help  nephrologists  manage patients into
the normal serum phosphorus range.

         Renagel's growth will also be driven by a substantial increase in the
number of patients undergoing dialysis. Worldwide, approximately 1 million
people are now on dialysis and the number is expected to reach 1.7 million by
2009, led by the increased incidence of diabetes, hypertension, and a growing
elderly population. The current annual cost of Renagel therapy is approximately
$1,000 per patient and is expected to double within the decade from a
combination of prescription-driven dosage increases and compliance improvements.
Based on market penetration estimates and the availability of reimbursement,
Genzyme expects Renagel revenues to reach $500 million within five years and $1
billion in ten years.

         Another major driver of Renagel's growth will be its potential to
improve patient morbidity and mortality. In a study to be published next month,
Dr. Allan Collins of the University of Minnesota showed a significant
improvement in morbidity and observed improved trends in mortality among
Medicare patients treated with Renagel compared with patients treated with
calcium binders. In this retrospective analysis of data from the U.S. Renal Data
System, Collins found a statistically significant 50 percent reduction in
hospitalization among Renagel patients compared to the calcium-treated patients.
He also observed a 35 percent reduction in deaths among Renagel patients,
although the small sample size studied did not allow Collins to confirm its
statistical significance. Collins' data has been presented at the 1999 American
Society for Nephrology meeting and the 2000 National Kidney Foundation meeting.

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Genzyme General to Acquire GelTex Pharmaceuticals--7

         Genzyme is currently designing--and plans to begin early next year--a
large, prospective, randomized, clinical trial designed to confirm the impact of
Renagel on patient morbidity and mortality.

         One of the more intriguing aspects of the Collins study was its
analysis of patient Medicare payment histories. In this analysis, Collins found
dramatic annual costs savings for patients treated with Renagel. These savings
averaged more than $17,000 per patient annually based on decreased
hospitalizations alone. Genzyme believes Renagel's ability to lower the overall
cost of care for dialysis patients will play a critical role in the product's
long-term growth.

         Finally, an additional and significant attribute of Renagel is that it
has been shown in clinical studies to dramatically lower LDL cholesterol while
increasing HDL cholesterol.

RENAGEL REVENUE GROWTH

         Renagel has generated average quarter-to-quarter revenue growth of 25
percent since its introduction. Renagel sales in 1999--the product's first full
year on the market--were $19.5 million. For 2000, Renagel sales are expected to
more than double, and Genzyme is now revising its revenue guidance upward, for
the second time this year, to around $45 million. Renagel revenues are expected
to double again in 2001 and--within five years--to exceed $500 million.

         Renagel is currently marketed in the United States, Europe, Canada, and
Israel under a 50/50 joint venture between Genzyme and GelTex. The product is
being developed and will be commercialized in Japan and other Pacific Rim
countries by Chugai Pharmaceuticals and Kirin Pharmaceuticals under agreements
with GelTex.

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Genzyme General to Acquire GelTex Pharmaceuticals--8

OTHER BENEFITS OF THE TRANSACTION

         In addition to Renagel, Genzyme's acquisition of GelTex will also give
it access to WelChol, three products in clinical trials and three more product
candidates potentially entering clinical trials next year.

         Genzyme will receive royalties from sales of WelChol, which is being
launched by Sankyo-Parke Davis this month. A Phase 2 clinical trial of a
second-generation version of WelChol will be completed this quarter and
additional clinical trials are planned.

         GelTex also has a number of exciting products in its pipeline. Its
leading product in development is a toxin binder known as GT160-246 for
CLOSTRIDIUM DIFFICILE (C. DIFFICILE), which is a major cause of antibiotic
associated colitis, a condition common in hospitals and nursing homes. C.
DIFFICILE affects over 500,000 patients per year, resulting in prolonged
hospital stays and increased costs, and is the cause of an estimated 5,000
deaths annually. A Phase 1 trial of GT160-246 in normal volunteers was completed
in August, and a Phase 2 clinical trial of the product is expected to begin
later this year.

         In addition, GelTex has made significant progress in its research
efforts toward discovery of a new class of fat-absorption inhibitors. GelTex has
identified a family of polymers that inhibit pancreatic lipase, the key enzyme
involved in fat digestion in the intestine. In pre-clinical studies, these
compounds have shown they can inhibit lipase with a potency in the range of that
of known inhibitors. They have also show that they can significantly inhibit fat
absorption. GelTex has also identified polymers that bind fat and prevent the
oily stool associated with lipase inhibition. Since these compounds are

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Genzyme General to Acquire GelTex Pharmaceuticals--9

high-molecular-weight polymers, they are unlikely to be absorbed into the blood
stream. Such compounds could potentially inhibit fat absorption without causing
oily stool side effects associated with current therapy.

         GelTex's robust polymer technology platform has produced two approved
products and several promising product candidates within a short six-year
timespan. Genzyme expects that this technology will be a consistent and
productive source of product candidates to feed its therapeutics pipeline.
Polymer technology has wide ranging applications, and polymer-based products
enjoy a relatively quick development pathway and have proven to be very safe.
GelTex's scientists are widely respected in the industry, and the company's two
most senior scientists recently received an award from the American Chemical
Society for their innovative application of polymer technology to the
development of therapeutic agents.

         Genzyme General develops and markets therapeutic products and
diagnostic products and services. Genzyme General has three therapeutic products
on the market and a strong pipeline of products in development focused on the
treatment of genetic disorders. Genzyme General is a division of the
biotechnology company Genzyme Corporation.

         GelTex develops and markets non-absorbed polymer drugs that bind and
eliminate targeted substances within the gastrointestinal tract. In addition,
GelTex is developing small-molecule pharmaceuticals consisting of novel
polyamine analogues and metal chelators.

          This press release contains forward-looking statements, including
statements about the consummation and anticipated timing of the merger, the
potential market opportunity for Renagel, the expected drivers of growth for the
market opportunity, the

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Genzyme General to Acquire GelTex Pharmaceuticals--10

anticipated impact of Renagel on Genzyme's future growth, the potential short
and long-term revenues from Renagel, the expected benefits of the merger, the
value of the merger consideration, the tax-free nature of the transaction, the
anticipated impact of the acquisition on Genzyme's earnings,
cash-earnings-per-share, and development programs, Genzyme's plans concerning
the operation of GelTex's business after the merger, estimates concerning the
current and future dialysis patient population, the anticipated impact of
Renagel on patient morbidity and mortality, the cost of care for patients, plans
to launch a new tablet formulation of Renagel, the anticipated benefits of the
tablet formulation, plans to announce trial data, plans to initiate clinical
trials of Renagel, GT 160-246, and other product candidates, estimates
concerning the C. Difficile Colitis patient population, expectations concerning
GelTex's product candidates and polymer technology platform. Actual results may
materially differ due to numerous factors, including without limitation
conditions in the financial markets relevant to the proposed merger, the receipt
of regulatory and other approvals of the transaction, the operational
integration associated with the transaction and other risks generally associated
with such transactions, increasing market acceptance of Renagel, increasing
doses of Renagel, market acceptance of Renagel tablets, the competitive
environment for the dialysis market, the results of clinical trials, the
efficacy and safety of products, enrollment rates for clinical trials, the
content and timing of submissions to and decisions by regulatory authorities,
the availability of reimbursement from third-party payers, the ability to
manufacture sufficient quantities of product for development and
commercialization activities, the accuracy of the companies' information about
the dialysis and the C. Difficile Colitis patient populations and the market for
Renagel, the accuracy of the companies' expectations about growth in the
dialysis patient population, the ability of Genzyme to successfully
commercialize products and the risks and uncertainties described in Genzyme and
GelTex's reports filed with the Securities and Exchange Commission under the
Securities Exchange Act of 1934, as amended, including without limitation
Exhibit 99.2 to Genzyme's Annual Report on Form 10-K for the year ended December
31, 1999, as amended. GENZ stock is a series of common stock of Genzyme
Corporation. Therefore, holders of GENZ stock are subject to the risks and
uncertainties described in the aforementioned reports.

         This material is not a substitute for the prospectus/proxy statement
Genzyme and GelTex will file with the Securities and Exchange Commission.
Investors are urged to read that document because it will contain important
information, including detailed risk factors. The proxy statement/prospectus and
other documents filed by Genzyme and GelTex with the SEC will be available free
of charge at the SEC's website (www.sec.gov) and from Genzyme or GelTex.

         GelTex, its directors, and certain of its executive officers may be
considered participants in the solicitation of proxies in connection with the
merger. Information concerning GelTex's directors and executive officers can be
found in the documents filed by GelTex with the SEC. Certain directors and
executive officers of GelTex may have direct or indirect interests in the merger
due to securities holdings, vesting of options, and rights to severance payments
if their employment is terminated following

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Genzyme General to Acquire GelTex Pharmaceuticals--11

the merger. In addition, directors and officers, after the merger, will be
indemnified by Genzyme, and benefit from insurance coverage, for liabilities
that may arise from their service as directors and officers of GelTex prior to
the merger. Additional information regarding the participants in the
solicitation will be contained in the proxy statement/prospectus.

                                     # # #

There will be a conference call beginning at 9:00 a.m. EDT today to discuss this
morning's news announcement regarding Genzyme General's (Nasdaq: GENZ) proposed
acquisition of GelTex Pharmaceuticals, Inc. (Nasdaq: GELX).

If you would like to participate in this call, please dial 212-346-0257
beginning at 8:45 a.m. EDT. A replay of this call will be available from 12:30
p.m. EDT on September 11 through 12:00 p.m. midnight on September 18 by calling
800-633-8284 in the U.S., or 619-812-6440 outside the U.S., reference
confirmation #16318162.

A replay of this call will also be broadcast over the internet at 1:00 p.m. EDT
today on Genzyme's Web site: www.genzyme.com. The replay of the call will be
available through midnight EDT September 25.

Genzyme's releases are available on the World Wide Web at
http://www.genzyme.com. They are also available from Genzyme's fax-on-demand
service at 1-800-436-1443 within the United States or 1-201-521-1080 outside
the United States.

GelTex's press releases are available at http://www.geltex.com



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