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                                                                      EXHIBIT 99

                        GENZYME TRANSGENICS CORPORATION
             IMPORTANT FACTORS REGARDING FORWARD-LOOKING STATEMENTS
                                   APRIL 2000

    IN THIS EXHIBIT 99, "WE," "US," "OUR" AND "GTC" REFER TO GENZYME TRANSGENICS
CORPORATION 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 or
concerning projected plans, performance, contract procurement 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. The words or phrases "will likely result,"
"are expected to," "will continue," "is anticipated," "estimate," "project," or
similar expressions are intended to 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 wish to 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 wish to 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 current 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 January 2,
2000, we have incurred cumulative losses of approximately $65.6 million. These
losses have resulted principally from the costs of our research activities and
expenses in excess of revenues from our contract research organization ("CRO")
services. Our primary sources of revenue have been our research and development
contracts and CRO services. To date, those revenues have not generated profits.
We expect to continue incurring significant operating losses until our product
sales and CRO service revenues sufficiently fund our operations. We cannot be
certain that we will become profitable.

WE FACE UNCERTAINTY IN RAISING ADDITIONAL FUNDS NECESSARY TO FUND OUR
OPERATIONS.

    In order to develop and bring our transgenic products to market, we and our
partners must commit substantial resources to costly and time consuming
research, preclinical testing and clinical trials. If our businesses do not
become profitable before we exhaust existing resources, we will need to obtain
additional financing, through public or private sources, including debt or
equity financings, or through collaborative or other arrangements with corporate
partners. We may not be able to obtain adequate funds for our operations from
these sources when needed or on acceptable terms. If we raise additional capital
through the sale of equity, or securities convertible into equity, your
proportionate ownership in GTC may be diluted. If we cannot obtain additional
financing, we could be forced to delay, scale back or eliminate some of our
research and development programs. In order to conserve capital or reduce our
reliance on
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obtaining new capital, we may also elect to delay or forgo timely expansion,
improvement or investment in our CRO services or dispose of the assets related
to those services.

    These forward-looking statements regarding our expected need for additional
funds are subject to risks and uncertainties. Our cash requirements may vary
materially from those now planned, depending upon the results of existing
businesses, the terms of future collaborations, results of research and
development, competitive and technological advances, regulatory requirements and
other factors.

TRANSGENIC TECHNOLOGY IS IN A RELATIVELY EARLY STAGE.

    Developing products based on transgenic technology is subject to significant
technological risks. Most of our transgenic proteins are in the early
development stage and will require time consuming and costly development,
testing and regulatory clearance. We have not, nor to our knowledge, has any
other entity completed human clinical trials necessary to receive marketing
authorization for any protein produced in the milk of transgenic animals. We
cannot be certain that we will be able to do so successfully, nor can we assure
that any transgenically produced protein will be safe or effective. In addition,
it is possible that research and discoveries by others will render our
transgenic technology obsolete or noncompetitive.

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.

    Obtaining required regulatory approvals for our transgenically produced
products may take several years to complete and may consume substantial capital
resources. We cannot give any assurance that the FDA or any other regulatory
authority will act quickly or favorably on our requests for approval, or that
the FDA or any other regulatory authority will not require us to provide
additional data that we do not currently anticipate in order to obtain
approvals. We cannot apply for FDA approval to market any of our products under
development until the product successfully completes its preclinical and
clinical trials. Several factors could prevent successful completion or cause
significant delays of these trials, including an inability to enroll the
required number of patients or failure to demonstrate adequately that the
product is safe and effective for use in humans. If safety concerns develop, the
FDA could stop our trials before completion. Moreover, to our knowledge, no
protein produced in the milk of a transgenic animal has reached the stage in the
regulatory process which would allow it to be submitted to the FDA for final
regulatory approval. 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 such animals. If we
are not able to obtain regulatory approvals for use of our products under
development, or if the patient populations for which they are approved are not
sufficiently broad, the commercial success of our products could be limited.

WE CANNOT ASSURE THE COMMERCIAL SUCCESS OF TRANSGENIC PRODUCTS.

    Even if our transgenically produced products are successfully developed and
approved by the FDA and corresponding 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:

    - possible 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;

    - the number and relative efficacy of competitive products that may
      subsequently enter the market; and
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    - 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 and implementing a commercialization
strategy for any transgenic products.

IF WE OBTAIN REGULATORY APPROVAL OF OUR TRANSGENIC PRODUCTS, THE PRODUCTS WILL
BE SUBJECT TO CONTINUING REVIEW AND EXTENSIVE REGULATORY REQUIREMENTS WHICH
COULD AFFECT THEIR MANUFACTURE AND MARKETING.

    The FDA and foreign regulatory agencies continue to review products even
after they have received initial approval. If and when the FDA or other agency
approves any of our transgenic products under development, the manufacture and
marketing of these products will be subject to continuing regulation, including
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 in the event we significantly alter 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, the occurrence of
unanticipated problems with products following approval, or for other reasons.
Any of these withdrawals could adversely affect our operating results.

WE DEPEND ON COLLABORATION AGREEMENTS FOR OUR REVENUE.

    Our revenue stream and our business strategy depend largely on our entering
into transgenic development agreements with third parties. We may not be able to
establish these agreements, and we cannot guarantee that we will establish our
agreements on commercially acceptable terms. Our future agreements may not
ultimately be successful. Even if we enter into transgenic development
agreements, our partners could terminate these agreements or they could expire
before meaningful developmental milestones are reached. The termination or
expiration of any of these agreements could have a material adverse effect on
our business.

    Much of the revenue that we may receive under these collaborations will
depend upon our partners' ability to successfully develop and commercially
introduce, market and sell new products derived from our transgenic production
systems. Our partners may develop competitive production technologies or
competitive products outside of their collaborations with us that could have a
material adverse effect on our business.

    To date, the scope of our collaboration agreements have generally been
limited to transgenically producing limited quantities of targeted proteins. We
cannot be certain that these initial development projects will be successful or
lead to collaboration agreements to commercially produce any proteins. 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,
preclinical and clinical testing, regulatory approval, sales, marketing and
distribution of any transgenic product.

ASPECTS OF OUR OPERATIONS ARE DEPENDENT ON OUR RELATIONSHIP WITH GENZYME.

    We are developing ATIII, our lead compound, in a joint venture in which
Genzyme Corporation ("Genzyme") provides substantial funding. If Genzyme does
not agree to continue that funding, we might not be able to fund ATIII on our
own or obtain funding from another partner on acceptable terms. As of
January 2, 2000 we owed $15.8 million to a commercial bank, which debt is
guaranteed by Genzyme. When Genzyme's guaranty expires, we might not be able to
negotiate an extension or replacement of our credit facility on acceptable
terms.
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CONCENTRATION OF OWNERSHIP OF OUR STOCK COULD LEAD TO FAILURE TO MAXIMIZE STOCK
PRICE AND CONFLICTS OF INTEREST.

    Genzyme is our largest single stockholder, currently holding 8,476,386
shares of our common stock, which represents approximately 31% of our
outstanding common stock. In connection with the issuance of our Series B
convertible preferred stock in November 1999, we issued to Genzyme warrants to
purchase 85,324 shares of our common stock at $6.30 per share. Genzyme's
ownership interest gives it significant influence over certain matters requiring
our stockholders' approval, including electing directors, adopting or amending
certain provisions of our articles of organization or by-laws and approving or
preventing certain mergers or other similar transactions, such as a sale of
substantially all of our assets (including transactions that could give our
stockholders the opportunity to realize a premium over the then-prevailing price
for their shares).

    Furthermore, Genzyme's ownership position may effectively discourage a third
party from making an acquisition proposal. Accordingly, this may inhibit a
change of control in circumstances that could give the holders of our common
stock the opportunity to realize a premium over the then-prevailing market
price, affect the market price of our common stock, or both. Our stockholders
other than Genzyme will be minority equity holders and will be unable to
significantly influence our management or business policies. Four of eight
members of our board of directors also serve as directors and/or executive
officers of Genzyme. The interests of Genzyme and GTC may differ from time to
time.

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 competitive. We will need to continue to devote substantial efforts
and expense to research and development in order to maintain a competitive
position. It is possible that developments by others will render our current and
proposed services, products or technologies obsolete. In addition, we may
encounter significant competition for protein development and production
contracts from other companies. Transgenic products may face significant
competition from biological products manufactured in cell culture or by other
traditional protein production methods. Our businesses will compete both against
other companies whose business is dedicated to offering transgenic production or
preclinical testing and development as a service, and with prospective customers
or collaborators who decide to pursue such transgenic production or preclinical
testing and development internally. Many of these competitors have greater
financial and human resources and more experience in research and development
than we have. 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.

THE PUBLIC MAY HAVE CONCERNS ABOUT GENETIC ENGINEERING IN ANIMALS AND ANIMAL
TESTING.

    Many of our activities involve genetic engineering in animals and animal
testing. These types of activities have been the subject of controversy and
adverse publicity. Animal rights groups and various other organizations and
individuals have attempted to stop genetic engineering activities and animal
testing by pressing for legislation and regulation in these areas. To the extent
the activities of such groups are successful, they may adversely affect our
business.

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

    Sales of pharmaceutical products largely depend on the reimbursement of
patients' medical expenses by government health care programs and private health
insurers. Without the financial support of the government or third party
insurers, the market for transgenic products will be limited. We cannot be sure
that third party payors will reimburse sales of our transgenic products, or
enable us or our partners to sell them at profitable prices.

    The federal government and private insurers have considered ways to change,
and have changed, the manner in which health care services are provided and paid
for in the United States. In particular, these
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third party payors are increasingly attempting to contain health care costs by
limiting both coverage and the level of reimbursement for new therapeutic
products. In the future, it is possible that the government may institute price
controls and further limits on Medicare and Medicaid 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.

OUR BUSINESS EXPOSES US TO POTENTIAL SERVICE AND PRODUCT LIABILITY.

    The nature of our business exposes us to potential product and professional
liability risks which are inherent in the testing, production, marketing and
sale of human therapeutic products. While we have obtained product and
professional liability insurance under an insurance policy arrangement with
Genzyme and Genzyme's affiliates, we cannot be certain that our insurance
coverage will be sufficient to cover any claim. Uninsured product or service
liability could have a material adverse effect on our financial results.
Additionally, it is possible that any insurance will not provide us with
adequate protection against potential liabilities. Potential liability may arise
from our handling of clinical samples containing human blood and tissues, which
may contain human pathogens. It is also possible that liability may arise from
handling animal blood and tissue which may contain zoonotic pathogens. Although
such products are used only in the laboratory, inadvertent human contact may
occur.

QUALIFIED MANAGERIAL AND SCIENTIFIC PERSONNEL ARE SCARCE IN OUR INDUSTRY.

    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.

OUR CRO BUSINESS IS DEPENDENT ON CURRENT GOVERNMENT REGULATORY REQUIREMENTS.

    The market for our preclinical testing services depends on our maintaining
strict standards for the conduct of laboratory and clinical tests and related
procedures that are promulgated by governmental entities responsible for public
health and welfare, including the FDA and by regulatory authorities in other
countries. The process of obtaining these approvals varies according to the
nature and use of the product and routinely involves lengthy and detailed
laboratory and clinical testing and other costly and time-consuming procedures.
We offer customers of our preclinical testing and development services the
necessary expertise to comply with these complex regulations. If the regulatory
structure were to change in a way which reduced the need for such services, we
could be materially adversely affected.

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
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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 firm is highly uncertain and involves complex legal and factual
questions.

    We have been issued six patents and currently have 20 provisional or regular
applications solely owned by us and two regular applications co-owned with
others pending in the United States. Where appropriate there are counterparts in
other countries. We may not receive any issued patents based on pending or
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.

    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.

WE HAVE OBLIGATIONS TO ISSUE SHARES OF COMMON STOCK IN THE FUTURE WHICH 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 the prevailing
market price of the common stock. As of March 20, 2000, there were 28,487,880
shares of common stock outstanding. As of March 20, 2000, options to purchase an
aggregate of 2,427,249 shares of common stock at varying exercise prices were
outstanding; of such total, options for 1,291,388 shares were immediately
exercisable and such shares could be immediately resold into the public market.
All of the 8,476,386 shares of common stock held by Genzyme could be sold into
the public markets upon compliance with Rule 144. The 518,324 shares 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.
Another 478,000 shares of common stock are reserved for issuance upon exercise
of outstanding warrants, all of which are currently exercisable and 450,000 of
which can be sold into the public market under a currently effective
registration statement.

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

    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. Many factors
can have a significant adverse effect on our common stock's market price,
including:

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

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

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

    Our articles of organization, certain provisions of our by-laws and certain
provisions of Massachusetts law could delay or make more difficult a merger,
tender offer or proxy contest involving us. These provisions may have the effect
of delaying or preventing a change of control without action by the stockholders
and, therefore, could adversely affect the price of our common stock.