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                                                                      EXHIBIT 99

                            GTC BIOTHERAPUETICS, INC.

             Important Factors Regarding Forward-Looking Statements

                                   March 2004

In this Exhibit 99, "we," "us," "our" and "GTC" refer to GTC Biotherapeutics,
Inc. and its subsidiaries.

From time to time, we may make forward-looking public statements, such as
statements concerning our then expected future revenues or earnings, prospects
for clinical trials or regulatory approvals, or our projected plans for research
and development programs and collaborations, as well as other estimates relating
to future operations. Forward-looking statements may be in reports filed under
the Securities Exchange Act of 1934, as amended (the "Exchange Act"), in press
releases or informal statements made with the approval of an authorized
executive officer. In some cases, words or phrases of expectation or uncertainty
like "expect," "believe," "continue," "anticipate," "estimate," "may," "will,"
"could," "opportunity," "future," "project," or similar expressions identify
"forward-looking statements" within the meaning of Section 21E of the Exchange
Act and Section 27A of the Securities Act of 1933, as amended, as enacted by the
Private Securities Litigation Reform Act of 1995.

We caution you not to place undue reliance on these forward-looking statements,
which speak only as of the date on which they are made. In addition, we advise
you that the factors listed below, as well as other factors we have not
currently identified, could affect our financial or other performance and could
cause our actual results for future periods to differ materially from any
opinions or statements expressed with respect to future periods or events in any
forward-looking statement.

We will not undertake and specifically decline any obligation to publicly
release revisions to these forward-looking statements to reflect either
circumstances after the date of the statements or the occurrence of events which
may cause us to re-evaluate our forward-looking statements.

In connection with the "safe harbor" provisions of the Private Securities
Litigation Reform Act, we are hereby filing cautionary statements identifying
important factors that could cause our actual results to differ materially from
those projected in forward-looking statements made by us or on our behalf.

WE EXPECT TO INCUR FUTURE OPERATING LOSSES AND MAY NEVER BECOME PROFITABLE.

We have had operating losses since our inception, and we expect losses to
continue for the next several years. From our inception in 1993 to December 28,
2003, we have incurred cumulative losses of approximately $150 million. Our net
losses for fiscal years ended 2001, 2002 and 2003 have been $16.6 million, $24.3
million, and $29.5 million, respectively. These losses have resulted principally
from the costs of our research and development activities and losses from our
discontinued operations. We expect to continue incurring significant operating
losses for at least the next several years as we incur increased costs and
expenses associated with clinical trials and

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submissions for regulatory approvals. We may never receive material revenues
from product sales or become profitable.

WE DEPEND ON COLLABORATION AGREEMENTS FOR OUR CURRENT REVENUE.

Our revenues and business strategy depend largely on our entering into
additional transgenic development agreements with third parties, even in the
case of development programs for our own therapeutic compounds. We may not be
able to establish these agreements on commercially acceptable terms, if at all,
depending on the market position of our technology. The willingness of potential
collaborators depends on factors such as the perceived technological or economic
advantages of transgenic production and our ability to structure a mutually
acceptable collaboration arrangement. In the case of our own programs for
development of proteins proprietary to us, known as internal programs, the
attractiveness of the program's commercial potential or other advantages the
program offers the partner will also affect our ability to obtain collaborators.
Even if we enter into transgenic development agreements, the collaborations may
ultimately be unsuccessful, our partners could terminate the agreements or the
agreements could expire before meaningful developmental milestones are reached.
The failure of any significant number of these collaborations could have a
material adverse effect on our business.

The majority of our collaborations are, and will likely continue to be, external
programs that involve proteins proprietary to our partners. Much of the revenue
that we may receive under these collaborations will depend upon our partners'
willingness and ability to successfully develop and commercially introduce,
market and sell the version of the collaborator's product derived from our
transgenic production systems in goats and other mammals. Our partners may
develop competitive production technologies or competitive products outside of
their collaborations with us, which could have a material adverse effect on our
business.

To date, the scope of our collaboration agreements have generally been limited
to transgenically producing quantities of targeted proteins. These initial
development projects may not successfully produce the desired protein quantities
or lead to collaboration agreements to commercially produce any proteins. The
success of any collaboration ultimately will be dependent upon our collaborator
deciding to seek regulatory approval and to market our transgenically produced
version of their product or to invest in a transgenic product that we have
developed. Depending upon the terms of any future collaborations, our role in
the collaboration will often be limited to the production aspects of the
proteins. As a result, we may also be dependent on collaborators for other
aspects of the development of any transgenic product, including preclinical and
clinical testing and regulatory approval, and marketing and distribution of any
transgenic product.

WE FACE UNCERTAINTY IN RAISING ADDITIONAL FUNDS FOR OUR OPERATIONS.

In order to develop and bring our transgenic products to market, we and our
collaboration partners must commit substantial resources to costly and time
consuming research, preclinical testing and clinical trials. As of December 28,
2003, we had $6.7 million in cash and cash equivalents and $24.4 million in
marketable securities, which were offset in part by our $10.3 million in current
liabilities. We expect our current cash resources and partnering revenue
opportunities will be sufficient to fund operations into 2005. Our projected
revenue and cash use depends upon attracting additional partnering revenues from
existing and additional collaborations. If we do not

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substantially achieve our revenue projections, we could be forced to delay,
scale back or eliminate one or more of our research and development programs.

Our cash requirements may vary materially from those now planned, depending upon
the results of research and development, competitive and technological advances,
the terms of future collaborations, regulatory requirements and other factors.
If our business does not become profitable before we exhaust existing resources,
we will need to obtain additional financing, through public or private sources,
including debt or equity financing, or through collaborative or other
arrangements with corporate partners. Depending on the state of the capital
markets, interest rates, our financial profile and other factors at that time,
we may not be able to obtain adequate funds on acceptable terms when needed. If
we raise capital through the sale of equity, or securities convertible into
equity, existing stockholders' proportionate ownership in us will be diluted. If
we cannot obtain financing, we could be forced to delay, scale back or eliminate
some of our research and development programs.

TRANSGENIC TECHNOLOGY IS IN A RELATIVELY EARLY STAGE.

Developing products based on transgenic technology is subject to significant
technological risks. Most of our transgenic protein products are in the early
development stage. Each DNA construct is unique and it is possible that it might
not be expressed in the transgenic animal's milk at a level that is commercially
viable. Purifying the recombinant protein out of the milk to use as a
biotherapeutic may be too difficult to be commercially feasible. In addition,
production of the recombinant protein may have negative effects on the health of
either the mammary gland or more systematically on the animal as a whole. This
would compromise the ability of the animal to produce the recombinant protein.
Directing the mammary gland to produce additional proteins in the milk could
negatively effect lactation, thereby shutting down milk production. The mammary
gland may also modify a protein in such a manner that it is non-functional or
harmful to human subjects. It is also possible that there may be disease agents
present in goats or cows that would prevent the use of products derived from
these animals. If an as yet unknown disease was identified in these animals and
government agencies banned the use of animal products, recombinant proteins from
milk could not be used.

To our knowledge, no other entity has completed human clinical trials necessary
to receive marketing authorization for any protein produced in the milk of
transgenic animals and until European regulatory authorities approve our
application for marketing authorization of ATryn(R) in Europe, we will not have
confirmation that our ATryn(R) trials are sufficient for approval in Europe. If
we are unable to complete all clinical trials that may be required, or if a
transgenically produced protein is not proved to be safe or effective, it would
have a material adverse effect on our business and operations. In addition, it
is possible that research and discoveries by others could render our transgenic
technology obsolete or noncompetitive as a method of production for
protein-based therapeutic products.

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IF CLINICAL TRIALS OF ANY OF OUR TRANSGENIC PRODUCT CANDIDATES ARE UNSUCCESSFUL
OR DELAYED, WE WOULD BE UNABLE TO MEET OUR ANTICIPATED DEVELOPMENT TIMELINE,
WHICH COULD CAUSE OUR STOCK PRICE TO DECLINE.

We and our collaborators must demonstrate through preclinical and clinical
trials that our transgenic product candidates are safe and effective for use in
humans. Clinical trials are expensive and may take several years. Several
factors could prevent or delay completion of these trials, including an
inability to enroll the required number of patients or demonstrate adequately
the safety or efficacy of the product for humans. If safety concerns develop,
regulatory authorities could stop our trials. Furthermore, the results from
early clinical trials are often not predictive of results in later clinical
trials.

WE CANNOT MARKET AND SELL OUR TRANSGENIC PRODUCTS IN THE UNITED STATES OR IN
OTHER COUNTRIES IF WE FAIL TO OBTAIN THE NECESSARY REGULATORY APPROVALS.

Before we can sell any transgenically produced drug or biological products
that we or our collaborators develop, we must receive regulatory approvals by
federal, state and local governmental authorities, including the United
States Food and Drug Administration, or FDA, and similar agencies in other
countries. To date, none of our transgenically produced products have been
approved for sale in the United States or any foreign country. Moreover, to
our knowledge, no therapeutic protein produced in the milk of a transgenic
animal has been submitted to the FDA for final regulatory approval or, except
for our submission of Atryn(R) to the EMEA in January 2004, to any other
regulatory agency for final regulatory approval. Obtaining required
regulatory approvals for our transgenically produced products may take
several years to complete and is expensive and uncertain. It is possible that
the FDA or any other regulatory authority may not act quickly or favorably on
our requests for approval or will require us to provide additional data that
we do not currently anticipate. For example, the FDA may impose restrictions
and demands on our clinical trials that require additional resources and
result in longer delays than we anticipate. In addition, the FDA may require
us to conduct further clinical trials and post-marketing testing and
surveillance to monitor the effects of approved products. The FDA or other
regulatory authorities may also place conditions on approval that could
restrict the commercial applications of such products.

Failure to comply with extensive FDA or similar regulations may result in delay,
suspension or cancellation of a trial or a regulatory authority's refusal to
accept test results. Regulatory authorities may have varying interpretations of
our pre-clinical and clinical trial data, which could delay, limit or prevent
regulatory approval or clearance. Because transgenic products represent novel
therapeutic products, the process for regulatory approval is unproven. There may
be additional delays in regulatory approval due to issues arising from the
breeding of transgenic animals and the use of proteins derived from them. Any
delays or difficulties in obtaining regulatory approval or clearance for
transgenically produced products may:

     -   adversely affect the marketing of any transgenic products we or our
         collaborators develop;

     -   impose significant additional costs on us or our collaborators;

     -   diminish any competitive advantages that we or our collaborators may
         attain; and

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     -   limit our ability to receive royalties and generate revenue and
         profits.

If we do not receive regulatory approvals for our transgenically produced
products in a timely manner, we will not be able to commercialize our products,
or their commercialization may be limited or delayed and, therefore, our
business and stock price will suffer.

Even if we receive regulatory approval for our transgenically produced products,
the FDA or similar agencies in other countries may impose limitations on the
indicated uses for which our products may be marketed. These limitations could
reduce the size of the potential market for a product. Failure to comply with
applicable FDA and other regulatory requirements can result in, among other
things, warning letters, fines, injunctions, civil penalties, recall or seizure
of products, total or partial suspension of production, refusal of the
government to renew our marketing applications and criminal prosecution.

We are in discussions with the FDA regarding our clinical and regulatory
strategy for approval of ATryn(R) in the United States. In response to an
investigational new drug application, or IND, filed with the FDA in 2003 for
clinical development of ATryn(R) in the hereditary deficiency indication, the
FDA has provided us guidance that it wishes to see a controlled study as a basis
for approval, which may not be feasible for this indication. Such a study has
not been required under the advice we have received from the European regulatory
authority for approval of ATryn(R) in the hereditary deficiency indication in
Europe. We are in a continuing dialogue with the FDA to define an appropriate
clinical and regulatory strategy for ATryn(R) approval in hereditary deficiency
or another indication that meets the agency's requirements. We intend to move
forward with our clinical development program for ATryn(R) in the United States
in 2004 under an appropriate IND once agreement has been reached with the FDA.
Until we know the nature of any clinical program that may be agreed with the
FDA, we are unable to estimate a timetable for filing a Biologics License
Application on ATryn(R) in the United States. If we do not reach agreement with
the FDA on an appropriate IND for ATryn(R), we will not be able to proceed with
its clinical development in the United States.

ANY TRANSGENIC PRODUCTS FOR WHICH WE OBTAIN REGULATORY APPROVAL WILL BE SUBJECT
TO CONTINUING REVIEW AND EXTENSIVE REGULATORY REQUIREMENTS, WHICH COULD AFFECT
THEIR MANUFACTURE AND MARKETING.

If and when the FDA or other foreign agencies approve any of our transgenic
products under development, the manufacture and marketing of these products will
be subject to continuing regulation and product approvals may be withdrawn if
problems occur after initial approval. Post-approval regulation includes
compliance with current Quality Systems Regulations and Good Manufacturing
Practices, known as QSR/GMP, adverse event reporting requirements and
prohibitions on promoting a product for unapproved uses. We will also be
required to obtain additional approvals for any significant alterations in the
product's labeling or manufacturing process. Enforcement actions resulting from
failure to comply with QSR/GMP requirements could result in fines, suspensions
of approvals, recalls of products, operating restrictions and criminal
prosecutions, and affect the manufacture and marketing of our transgenic
products. The FDA or other regulatory agencies could withdraw a previously
approved product from the market upon receipt of newly discovered information,
including a failure to comply with regulatory requirements and the occurrence of
unanticipated problems with products following approval. Any of these
withdrawals could adversely affect our operating results.

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WE HAVE LIMITED MANUFACTURING CAPABILITY AND MAY RELY ON THIRD PARTY CONTRACT
MANUFACTURERS TO PURIFY AND FORMULATE OUR TRANSGENIC PRODUCTS.

We have the capability to purify pre-clinical and clinical trial quantities of
our transgenic product candidates. Our current capacity allows us to purify
products for clinical trials, up to and including phase II. We also rely upon
third party manufacturers to purify and formulate significant pre-clinical and
clinical quantities of our transgenic product candidates from the milk of our
transgenic animals. We will depend on these third party manufacturers to perform
their obligations in a timely manner and in accordance with applicable
government regulations in order to conduct our clinical trials or commercialize
any of our products. In addition, there are very few third party manufacturers
that have sufficient production capacity to manufacture all of our product
candidates either for our clinical trials or on a commercial scale. Our third
party manufacturers may encounter difficulties, including problems involving:

     -   inconsistent production yields;

     -   poor quality control and assurance or inadequate process controls; and

     -   lack of compliance with FDA and other regulations.

These contract manufacturers may not be able to manufacture our product
candidates at a cost or in quantities necessary to make them commercially
viable. If we are unable to enter into agreements with additional manufacturers
on commercially reasonable terms, or if there is poor performance on the part of
our third party manufacturers, we may not be able to complete development of, or
market, our transgenic product candidates.

We have entered into a contract with Cambrex Bio Science MA, Inc. for the large
scale purification of our lead product candidate, ATryn(R). We have a five year,
renewable supply agreement with Cambrex, which will expire in 2007 if not
renewed. Although we have identified possible alternative suppliers with respect
to the purification of this product, interruptions in these services and the
process of changing to an alternative manufacturer could have a material adverse
effect on our timely ability to manufacture bulk delivery of ATryn(R) for
delivery to our collaborators.

TRANSGENIC PRODUCTS MAY NEVER BECOME COMMERCIALLY SUCCESSFUL.

Even if our transgenically produced products are successfully developed and
approved by the FDA and foreign regulatory agencies, they may not enjoy
commercial acceptance or success, which would adversely affect our business and
results of operations. Several factors could limit our success, including:

     -   limited market acceptance among patients, physicians, medical centers
         and third party payors;

     -   our inability to access a sales force capable of marketing the product;

     -   our inability to supply a sufficient amount of product to meet market
         demand;

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     -   the number and relative efficacy of competitive products that may
         subsequently enter the market; and

     -   for a transgenic product designed to replace or supplement currently
         marketed non-transgenic products, the relative risk-benefit profile and
         cost-effectiveness of the transgenically produced product.

In addition, it is possible that we or our collaborative partners will be
unsuccessful in developing, marketing or implementing a commercialization
strategy for any transgenic products.

OUR BUSINESS MAY FAIL DUE TO INTENSE COMPETITION IN OUR INDUSTRY.

The industries in which we operate are highly competitive and may become even
more so. Some of our competitors have greater financial and human resources and
more experience in research and development than we have. We will need to
continue to devote substantial efforts and expense in research and development
to maintain a competitive position for our transgenic production technology and
potential product offerings. It is also possible that others will develop
alternative technologies or products that will render our proposed products or
technologies obsolete. We may encounter significant competition for our protein
development and production contracts from other companies. In addition, our
potential transgenic production capabilities may face significant competition
from biological products manufactured in cell culture or by other traditional
protein production methods. Our business will also compete against other
companies whose business is dedicated to offering transgenic production and with
prospective customers or collaborators who decide to pursue such transgenic
production internally. Competitors that complete clinical trials, obtain
regulatory approvals and begin commercial sales of their products before us will
enjoy a significant competitive advantage. We anticipate that we will face
increased competition in the future as new companies enter the market and
alternative technologies become available.

Two other companies known to GTC are extensively engaged in the application of
transgenic technology in mammals for the production of proteins for therapeutic
use in humans: Pharming Group N.V. and PPL Therapeutics plc. Pharming, based in
the Netherlands, is primarily engaged in the development of recombinant proteins
in the milk of transgenic cows and rabbits. Pharming has one product in clinical
development that is in phase II studies. PPL, now in liquidation, is based in
Scotland and utilizes primarily sheep for transgenic protein production. PPL has
developed recombinant alpha-1 antitrypsin into phase II stage of clinical
testing. There are also other companies seeking to develop transgenic technology
in animals and in plants, which may be competitive with our technology with
respect to our patents and proprietary rights as discussed further below.

For ATryn(R), a number of companies internationally produce and market
antithrombin from the fractionation of human plasma. Aventis has approximately a
40% share of this market worldwide. Bayer is the only company that has
commercially available fractionated antithrombin material that is approved for
sale in the U.S., which sales represent only about 1% of the worldwide market.

There are a number of companies worldwide that produce and market human serum
albumin from the fractionation of human plasma. We estimate that Bayer and
Aventis sales represent approximately a 30% and 10% share, respectively, of the
worldwide market for human serum

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albumin. We are aware of two companies internationally that are developing
recombinant forms of human serum albumin derived from yeast cultures. One
company, Aventis, is developing its recombinant albumin product for the
excipient market.

WE MAY FACE PUBLIC CONCERNS ABOUT GENETIC ENGINEERING IN ANIMALS.

Our activities involve genetic engineering in animals. The commercial success of
our potential products will depend in part on public acceptance of the use of
genetic engineering. Public attitudes may be influenced by claims that these
types of activities are unsafe and our products may not gain the acceptance of
the public or the medical community. Negative public reaction to genetic
engineering activities in general could result in greater restrictive
legislation and regulations involving nuclear transfer and other methodologies
which could impede our ability to conduct efficiently our business, delay
preclinical studies or future clinical trials, or prevent us or our partners
from obtaining regulatory approvals or commercializing transgenically produced
products.

WE DEPEND ON PATENTS AND PROPRIETARY RIGHTS THAT MAY FAIL TO PROTECT OUR
BUSINESS.

Our success will partly depend on our ability to obtain and maintain patent or
other proprietary protection for our technologies, products and processes such
as:

     -   compositions of matter or processes;

     -   processes developed by our employees; or

     -   uses of compositions of matter discovered through our technology.

We may not be able to obtain the necessary protection. Our success will also
depend on our ability to operate without infringing the proprietary rights of
other parties. Legal standards relating to the validity of patents covering
pharmaceutical and biotechnological inventions and the scope of claims made
under these patents are still developing. There is no consistent policy
regarding the breadth of claims allowed in biotechnology patents. The patent
position of a biotechnology company is highly uncertain and involves complex
legal and factual questions.

     As of March 1, 2004, we hold 17 issued or allowed U.S. patents and 111
corresponding foreign patents. Our patents generally expire between 2013 and
2019, with the most significant patent expiring in 2015. In accordance with
ongoing research and development efforts, we have 40 pending U.S. patent
applications and 174 corresponding foreign applications covering relevant and
newly developed portions of its transgenic technology. Several of these pending
applications are included in various cross-licensing or out-licensing
arrangements with other companies that in turn provide access to their
proprietary technologies. Specifically we have cross-licensed our proprietary
technology for the production of proteins in milk to Pharming B.V. and PPL.
Recently issued U.S. patents provide claim coverage for protein purification
from the milk of transgenic animals, the production of monoclonal and assembled
antibodies at commercial levels in the milk of transgenic mammals, the
production of recombinant antithrombin in the milk of transgenic goats and the
production of Prolactin in the milk of transgenic animals. We cannot be certain
that we will receive issued patents based on pending or

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future applications. Our issued patents may not contain claims sufficiently
broad to protect us against competitors with similar technology. Additionally,
our patents, our partners' patents and patents for which we have license rights
may be challenged, narrowed, invalidated or circumvented. Furthermore, rights
granted under patents may not provide us with any competitive advantage.

We may have to initiate arbitration or litigation to enforce our patent and
license rights. If our competitors file patent applications that claim
technology also claimed by us, we may have to participate in interference or
opposition proceedings to determine the priority of invention. An adverse
outcome could subject us to significant liabilities to third parties and require
us to cease using the technology or to license the disputed rights from third
parties. We may not be able to obtain any required licenses on commercially
acceptable terms or at all.

The cost to us of any litigation or proceeding relating to patent rights, even
if resolved in our favor, could be substantial. Some of our competitors may be
able to sustain the costs of complex patent litigation more effectively than we
can because of their substantially greater resources. Uncertainties resulting
from the initiation and continuation of any pending patent or related litigation
could have a material adverse effect on our ability to compete in the
marketplace. The U.S. Patent and Trademark Office has declared an interference
proceeding between Advanced Cell Technologies, Inc. (ACT) and Geron Corporation
for one of the patents we license from ACT. While we have also licensed nuclear
transfer technology from Pharming, we do not know at this time what impact, if
any, this interference proceeding may have on our ability to practice nuclear
transfer for the production of animals expressing therapeutic proteins in their
milk.

We rely on certain proprietary trade secrets and know-how that are not
patentable. We have taken measures to protect our unpatented trade secrets and
know-how, including having our employees, consultants and some contractors
execute confidentiality agreements. These agreements could be breached. If so,
it is possible that our remedies for a given breach might be inadequate. It is
also possible that competitors could independently develop or discover our trade
secrets or that the trade secrets could otherwise become known.

RECOVERY FROM ANY CATASTROPHIC EVENT MAY NOT BE ADEQUATE.

While we have measures in place to minimize and recover from catastrophic events
that may substantially destroy our animal herd(s), these measures may not be
adequate to recover our production processes quickly enough to support critical
timelines, collaborator needs or market demands. These catastrophic events may
include diseases that breach our biosecurity measures or weather events such as
tornadoes, earthquakes or fires. In addition, these catastrophic events may
render some or all of the products at the affected facilities unusable.

SUCCESSFUL COMMERCIALIZATION OF OUR PRODUCTS WILL DEPEND ON OBTAINING COVERAGE
AND REIMBURSEMENT FOR USE OF THE PRODUCTS FROM THIRD-PARTY PAYORS.

Sales of pharmaceutical products depend largely on the reimbursement of
patients' medical expenses by government health care programs and private health
insurers. It is possible that third party payors will not reimburse sales of our
transgenic products. Reimbursement by third party payors depends on a number of
factors, including the payor's determination that use of the product

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is safe and effective, not experimental or investigational, medically necessary,
appropriate for the specific patient and cost-effective. Reimbursement in the
United States or foreign countries may not be available or maintained for any of
our product candidates. If we do not obtain approvals for adequate third party
reimbursements, we may not be able to establish or maintain price levels
sufficient to realize an appropriate return on our or our partners' investment
in product development. Any limits on reimbursement available from third party
payors may reduce the demand for, or negatively affect the price of, our or our
partners' products. Without the financial support of the government or third
party insurers, the market for transgenic products will be limited.

The U.S. federal government and private insurers are continually working on ways
to contain health care costs, particularly by limiting both coverage and the
level of reimbursement for new therapeutic products. The government or private
insurers may institute future price controls and other cost-containment measures
on Medicare, Medicaid and other health care insurance spending. These controls
and limits could affect the payments we collect from sales of our products.
Internationally, medical reimbursement systems vary significantly, with some
medical centers having fixed budgets, regardless of levels of patient treatment,
and other countries requiring application for, and approval of, government or
third party reimbursement. Even if we or our partners succeed in bringing
transgenic products to market, uncertainties regarding future health care
policy, legislation and regulation, as well as private market practices, could
affect our ability to sell our products in commercially acceptable quantities at
profitable prices.

THE MANUFACTURE AND SALE OF OUR PRODUCTS MAY EXPOSE US TO PRODUCT LIABILITY
CLAIMS FOR WHICH WE COULD HAVE SUBSTANTIAL LIABILITY.

We face an inherent risk of product liability exposure related to testing of our
transgenic product candidates in human clinical trials and will face even
greater risks when we commercialize our products derived from these product
candidates. An individual may bring a product liability claim against us if one
of our products or product candidates causes, or is claimed to have caused, an
injury or is found to be unsuitable for consumer use. Although we have obtained
product liability insurance under an insurance policy arrangement with Genzyme
Corporation and Genzyme's affiliates, it is possible that our insurance coverage
will not be sufficient to cover any claim. Any product liability claim brought
against us, with or without merit, could result in:

     -   liabilities that substantially exceed our product liability insurance,
         which we would then be required to pay from other sources, if
         available;

     -   an increase of our product liability insurance rates or the inability
         to maintain insurance coverage in the future on acceptable terms or at
         all;

     -   damage to our reputation and the reputation of our products, resulting
         in lower sales;

     -   regulatory investigations that could require costly recalls or product
         modifications; and

     -   the diversion of management's attention from managing our business.

QUALIFIED MANAGERIAL AND SCIENTIFIC PERSONNEL ARE SCARCE IN OUR INDUSTRY.

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We are highly dependent on the principal members of our scientific and
management staff. Our success will depend in part on our ability to identify,
attract and retain qualified managerial and scientific personnel. There is
intense competition for qualified personnel in our industry. We may not be able
to continue to attract and retain personnel with the advanced technical
qualifications or managerial expertise necessary for the development of our
business. If we fail to attract and retain key personnel, it could have a
material adverse effect on our business, financial condition and results of
operations. We have employment agreements with our executive officers, but these
agreements do not guarantee that they will remain employed with us in the
future. If we lose an executive officer, or a significant number of any of our
staff, or are unable to hire and retain qualified personnel, then our ability to
develop and commercialize our products and processes may be delayed or impaired.
We do not carry key man insurance.

GENZYME'S SIGNIFICANT OWNERSHIP INTEREST IN US COULD GIVE IT SIGNIFICANT
INFLUENCE OVER MATTERS REQUIRING STOCKHOLDER APPROVAL.

Genzyme is our largest single stockholder, beneficially owning 5,443,243 shares
or 16.8% of our outstanding common stock at December 28, 2003, assuming the
exercise of its 518,324 currently exercisable common stock purchase warrants
with exercise prices ranging from $6.30 to $2.84. As a 16.8% shareholder,
Genzyme's ownership interest could give it significant influence if it were to
oppose matters requiring our stockholders' approval, including electing
directors, adopting or amending provisions of our charter or by-laws and
approving or preventing some mergers or similar transactions, such as a sale of
substantially all of our assets, or transactions that could give our
stockholders the opportunity to realize a premium over the market price of their
shares.

WE HAVE OBLIGATIONS TO ISSUE SHARES OF COMMON STOCK IN THE FUTURE THAT WILL
DILUTE YOUR OWNERSHIP INTEREST AND MAY ADVERSELY AFFECT OUR STOCK PRICE.

Sales of substantial amounts of our common stock in the public market, or the
perception that such sales may occur, could adversely affect our common stock's
market price. As of December 28, 2003, there were 31,929,473 shares of our
common stock outstanding. As of December 28, 2003, options to purchase an
aggregate of 3,782,208 shares of common stock at varying exercise prices were
outstanding; of this total, options to purchase 2,230,035 shares were
immediately exercisable and these shares could be immediately resold into the
public market. As of December 28, 2003, Genzyme held 4,924,919 shares of our
common stock which could be sold into the public markets under Rule 144 of the
Securities Act, but which are currently subject to a lock-up provision until
April 2004. The lock-up provision will be released at an earlier date if the
average of the prices of our daily high and low stock prices, as reported on The
NASDAQ National Market, exceeds $12.00 per share for 20 consecutive trading
days. Genzyme is also entitled to registration rights with respect to some of
these shares. An additional 518,324 shares of our common stock, issuable to
Genzyme upon exercise of outstanding warrants, are also entitled to registration
rights, which could expedite the resale of such shares into the public market.

In August 2003, we completed a private placement transaction in which we sold
the Selling Stockholders 3,626,465 shares of our common stock and warrants to
purchase an aggregate 961,009 shares of our common stock at an exercise price of
$3.30 per share. We have registered for resale the shares of common stock and
the shares issuable under the warrants that were issued in the private placement
transaction.

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OUR CAPITAL RAISING EFFORTS MAY DILUTE STOCKHOLDER INTERESTS.

If we raise additional capital by issuing equity securities, the issuance will
result in ownership dilution to our existing shareholders. The extent of such
dilution will vary based upon the amount of capital raised.

OUR COMMON STOCK MAY HAVE A VOLATILE PUBLIC TRADING PRICE AND LOW TRADING
VOLUME.

Historically, the market price of our common stock has been highly volatile and
the market for our common stock has experienced significant price and volume
fluctuations, some of which are unrelated to our company's operating
performance. Since January 1, 2001, the trading price of our stock has
fluctuated from a high of $15.50 to a low of $0.61. It is likely that the market
price of our common stock will continue to fluctuate in the future. Factors
which may have a significant adverse effect on our common stock's market price,
include:

     -   announcements by us or our competitors of technological innovations or
         new commercial products;

     -   developments concerning our proprietary rights, including patent and
         litigation matters;

     -   publicity regarding actual or potential results relating to our or our
         partners' products or compounds under development;

     -   an unexpected termination of one of our partnerships;

     -   regulatory developments in the United States and other countries;

     -   general market conditions; and

     -   quarterly fluctuations in our revenues and other financial results.

The average daily trading volume of our common stock for the three-month period
ending February 24, 2004 was 239,136 shares.

ANTI-TAKEOVER PROVISIONS IN OUR CHARTER AND BY-LAWS AND MASSACHUSETTS LAW MAY
RESULT IN MANAGEMENT ENTRENCHMENT AND ADVERSELY AFFECT OUR STOCK PRICE.

Anti-takeover provisions in our charter, our by-laws and Massachusetts statutes
could delay or make more difficult a merger, tender offer or proxy contest
involving us. These provisions may delay or prevent a change of control without
action by the stockholders, and may resist important changes stockholders seek
to make if they are dissatisfied with the conduct of our management. Therefore,
these provisions could result in the entrenchment of our management and
adversely affect the price of our common stock.

Our charter grants authority to the board of directors to issue series of
preferred stock with certain rights and privileges, including voting rights, as
it deems appropriate. This authority may enable our board of directors to deter
or delay a change in control despite a shift in stock ownership, as a result of
an increase in the number of shares needed to gain voting control. This may have
the

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effect of discouraging tender offers and proxy contests, and give management the
power to reject certain transactions which might be desired by stockholders.
This provision could also be deemed to benefit incumbent management to the
extent it deters offers by persons who would wish to make changes in management
or exercise control over management.

In addition, our by-laws may have the effect of preventing changes in our
management because stockholders are required to give us written notice of any
proposal or director nomination within a specified period of time before the
annual meeting of stockholders, certain qualifications for a person to be
elected to the board of directors must be established, and stockholders are
prohibited from calling a special meeting of stockholders, unless the
stockholder owns 90% of our outstanding voting stock.

Our stockholder rights plan is another anti-takeover device. It involves a
distribution to our stockholders of certain rights to acquire shares of our
capital stock in the event of an acquisition of a predetermined number of shares
by an investor. The stockholder rights plan is designed to deter coercive
takeover tactics and to encourage a party interested in acquiring the
corporation to negotiate with the board of directors.

Certain Massachusetts corporate statutes provide anti-takeover protections. Our
charter gives effect to a provision of Massachusetts law that places directors
of publicly-held Massachusetts corporations into three classes of nearly equal
sizes with staggered terms, thereby permitting only one-third of the board of
directors to be elected at once. In addition, with certain exceptions,
Massachusetts law prohibits a publicly-held Massachusetts corporation from
engaging in a business combination transaction with an "interested stockholder"
for a period of three years. An "interested stockholder" is a person who owns 5%
or more of the outstanding voting stock of the corporation. Finally, our by-laws
include a provision excluding us from the applicability of a Massachusetts
statute that denies voting rights to any person acquiring 20% or more of the
outstanding voting stock of a corporation, unless such voting rights are
approved by a majority of the corporation's disinterested shareholders. Our
by-laws may be amended at any time to subject us to this statute prospectively.

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