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                                   EXHIBIT 99.1

                            GTC BIOTHERAPUETICS, INC.

             Important Factors Regarding Forward-Looking Statements

                                   March 2003

In this Exhibit 99.1, "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 29,
2002, we have incurred cumulative losses of approximately $120 million. 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
submissions for regulatory approvals. We may never receive material revenues
from product sales or become profitable.

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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 cannot
guarantee that we will be able to establish these agreements on commercially
acceptable terms, if at all. 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. 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 of any
transgenic product, including preclinical and clinical testing and regulatory
approval, and marketing and distribution of any transgenic product.

In the case of our collaboration with Merrimack Pharmaceuticals, our transgenic
version of its MM-093 product is the one that Merrimack intends to use in
clinical trials. As part of the collaboration we have agreed to allow Merrimack
to defer payment of the costs of development of the compound through June 2003,
subject in part to specified conditions. Re-payment of these advances is
substantially dependent upon Merrimack completing a further financing. We are
currently deferring recognition of revenue associated with the costs advanced to
Merrimack.

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. 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

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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 GTC 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. 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, nor that any transgenically produced protein will
be safe or effective. 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.

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 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 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. Obtaining required regulatory approvals for our
transgenically produced products may take several years to complete and is
expensive and uncertain. We cannot give any assurance that the FDA or any other
regulatory authority will act quickly or favorably on our requests for approval
or will not require us to provide additional data that we do not currently
anticipate.

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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 clearances 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

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

If we do not receive regulatory approval for our transgenically produced
products in a timely manner, we will not be able to commercialize our products,
and therefore, our business and stock price will suffer.

Even if we receive regulatory approval for our transgenically produced products,
the FDA 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.

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

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regulatory requirements and the occurrence of unanticipated problems with
products following approval. Any of these withdrawals could adversely affect our
operating results.

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. 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 products
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 CANNOT ASSURE THE COMMERCIAL SUCCESS OF TRANSGENIC PRODUCTS.

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;

       -    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.

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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 also is 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 and PPL. Pharming, based in the Netherlands, is
primarily engaged in the development of recombinant proteins in the milk of
transgenic cows and rabbits. PPL, based in Scotland, utilizes primarily sheep
for transgenic protein production. There are also other companies seeking to
develop transgenic technology in animals and in plants.

For rhATIII, Bayer in the U.S. and a number of companies internationally,
produce and market antithrombin from the fractionation of human plasma.
Similarly, there are a number of companies worldwide that produce and market
human serum albumin from the fractionation of human plasma. There are 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. We cannot be certain to
what extent these efforts will be successful.

Restrictive legislation and regulations involving nuclear transfer and other
methodologies could be developed which could impede our ability to efficiently
conduct our business, delay preclinical studies or future clinical trials, or
prevent us or our partners from obtaining regulatory approvals or
commercializing transgenically produced products.

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

Currently, we hold 11 issued U.S. patents and 42 corresponding foreign patents.
In accordance with ongoing research and development efforts, we have 3 pending
U.S. patent applications and 205 corresponding foreign applications covering
relevant and newly developed portions of its transgenic technology. Several of
these pending applications are included in cross-licensing arrangements with
other companies that in turn provide access to their proprietary technologies.
Recently issued GTC 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 ATIII in the milk of transgenic goats and one covering the
production of Prolactin in the milk of transgenic animals. We cannot be certain
that we will receive 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.

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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, 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. 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 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. We cannot be certain of the
extent to which the government or private insurers may institute future price
controls and other cost-containment measures on Medicare, a 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. While we have obtained
product liability insurance under an insurance policy arrangement with Genzyme
and Genzyme's

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affiliates, we cannot be certain that our insurance coverage will 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.

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.

GENZYME CORPORATION'S 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 19.2% of our outstanding common stock at December 29, 2002, assuming the
exercise of 518,324 currently exercisable common stock purchase warrants with
exercise prices ranging from $6.30 to $2.84. As a 19.2% 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 29, 2002, there were 27,759,064 shares of our
common stock outstanding. As of December 29, 2002, options to purchase an
aggregate of 3,178,219 shares of common stock at varying exercise prices were
outstanding; of this total, options to purchase 1,804,885 shares were
immediately exercisable and these shares could be immediately resold into the
public market. As of December 29, 2002, Genzyme held 4,924,919 shares of our
common stock which could be sold

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into the public markets under Rule 144 of the Securities Act. Genzyme is also
entitled to registration rights with respect to some of these shares. An
additional 518,324 shares are 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.

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;

       -    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.

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, therefore, could adversely affect the price of
our common stock.

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