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<PAGE>   1


     AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON AUGUST 10, 2001

                                                           REGISTRATION NO. 333-

                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION

                             WASHINGTON, D.C. 20549

                                    FORM S-3
                             REGISTRATION STATEMENT

                                      UNDER

                           THE SECURITIES ACT OF 1933

                          LEXICON GENETICS INCORPORATED
             (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)

                  DELAWARE                                76-0474169
      (STATE OR OTHER JURISDICTION OF                  (I.R.S. EMPLOYER
       INCORPORATION OR ORGANIZATION)               IDENTIFICATION NUMBER)

                                  ------------

                           4000 RESEARCH FOREST DRIVE
                           THE WOODLANDS, TEXAS 77381
                                 (281) 364-0100


  (ADDRESS, INCLUDING ZIP CODE, AND TELEPHONE NUMBER, INCLUDING AREA CODE, OF
                   REGISTRANT'S PRINCIPAL EXECUTIVE OFFICES)

                                  ------------

                          ARTHUR T. SANDS, M.D., PH.D.
                      PRESIDENT AND CHIEF EXECUTIVE OFFICER
                           4000 RESEARCH FOREST DRIVE
                           THE WOODLANDS, TEXAS 77381

                                 (281) 364-0100

 (NAME, ADDRESS, INCLUDING ZIP CODE, AND TELEPHONE NUMBER, INCLUDING AREA CODE,
                             OF AGENT FOR SERVICE)

                                  ------------

                                   COPIES TO:

         DAVID P. OELMAN                          JEFFREY L. WADE
      VINSON & ELKINS L.L.P.        EXECUTIVE VICE PRESIDENT AND GENERAL COUNSEL
1001 FANNIN, 2300 FIRST CITY TOWER         LEXICON GENETICS INCORPORATED
    HOUSTON, TEXAS 77002-6760                4000 RESEARCH FOREST DRIVE
          (713) 758-3708                     THE WOODLANDS, TEXAS 77381
                                                      (281) 364-0100


     APPROXIMATE DATE OF COMMENCEMENT OF PROPOSED SALE TO THE PUBLIC:
     As soon as practicable after this registration statement becomes effective.

     If the only securities being registered on this Form are being offered
pursuant to dividend or interest reinvestment plans, check the following box.[ ]

     If any of the securities being registered on this Form are to be offered on
a delayed or continuous basis pursuant to Rule 415 under the Securities Act of
1933, other than securities offered only in connection with dividend or interest
reinvestment plans, check the following box. [X]

     If this Form is filed to register additional securities for an offering
pursuant to Rule 462(b) under the Securities Act, please check the following box
and list the Securities Act registration statement number of the earlier
effective registration statement for the same offering.[ ]

     If this Form is a post-effective amendment filed pursuant to Rule 462(c)
under the Securities Act, check the following box and list the Securities Act
registration statement number of the earlier effective registration statement
for the same offering. [ ]

     If delivery of the Prospectus is expected to be made pursuant to Rule 434,
please check the following box. [ ]

                         CALCULATION OF REGISTRATION FEE

<TABLE>
<CAPTION>
                                                                      PROPOSED MAXIMUM     PROPOSED MAXIMUM
           TITLE OF EACH CLASS OF                 AMOUNT TO BE       AGGREGATE OFFERING       AGGREGATE          AMOUNT OF
        SECURITIES TO BE REGISTERED                REGISTERED        PRICE PER SHARE (1)  OFFERING PRICE (1)   REGISTRATION
                                                                                                                   FEE
<S>                                             <C>                  <C>                  <C>                  <C>
Common Stock, par value $0.001.............     3,527,991 shares           $8.925            $31,487,319          $7,872
</TABLE>

(1)  Estimated solely for the purpose of calculating the amount of the
     registration fee based on the high and low trading price for the common
     stock on August 6, 2001, in accordance with Rule 457(c) under the
     Securities Act.

     THE REGISTRANT HEREBY AMENDS THIS REGISTRATION STATEMENT ON SUCH DATE OR
DATES AS MAY BE NECESSARY TO DELAY ITS EFFECTIVE DATE UNTIL THE REGISTRANT SHALL
FILE A FURTHER AMENDMENT WHICH SPECIFICALLY STATES THAT THIS REGISTRATION
STATEMENT SHALL THEREAFTER BECOME EFFECTIVE IN ACCORDANCE WITH SECTION 8(A) OF
THE SECURITIES ACT OF 1933, AS AMENDED, OR UNTIL THE REGISTRATION STATEMENT
SHALL BECOME EFFECTIVE ON SUCH DATE AS THE COMMISSION, ACTING PURSUANT TO SAID
SECTION 8(A), MAY DETERMINE.
<PAGE>   2
The information in this prospectus is not complete and may be changed. We may
not sell these securities until the registration statement filed with the
Securities and Exchange Commission is effective. This prospectus is not an offer
to sell these securities and it is not soliciting an offer to buy these
securities in any state where the offer or sale is not permitted.

                  SUBJECT TO COMPLETION, DATED AUGUST 10, 2001

                                3,527,991 SHARES

                                 [LEXICON LOGO]

                          LEXICON GENETICS INCORPORATED

                                  COMMON STOCK

                               ------------------


         This prospectus relates to the resale of previously issued shares of
our common stock by selling stockholders. The selling stockholders are offering
up to 3,527,991 shares of our common stock.

         We will not receive any proceeds from the sale of the shares offered by
the selling stockholders.

         The selling stockholders may offer the shares from time to time through
public or private transactions at prevailing market prices, at prices related to
prevailing market prices or at privately negotiated prices.

         Our common stock is listed on The Nasdaq National Market under the
symbol "LEXG". The last reported sale price on August ___, 2001 was $___ per
share.

         INVESTING IN THE COMMON STOCK INVOLVES RISKS. SEE "RISK FACTORS"
BEGINNING ON PAGE 4.

         Neither the Securities and Exchange Commission nor any state securities
commission has approved or disapproved of these securities or determined if this
prospectus is truthful or complete. Any representation to the contrary is a
criminal offense.


                     The date of this prospectus is          , 2001.
<PAGE>   3
                                TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                                                           PAGE
                                                                                                           ----
<S>                                                                                                        <C>
         Lexicon Genetics Incorporated..................................................................    3
         Risk Factors...................................................................................    4
         Special Note Regarding Forward-Looking Statements..............................................   13
         Use of Proceeds................................................................................   13
         Selling Stockholders...........................................................................   13
         Plan of Distribution ..........................................................................   16
         Legal Matters .................................................................................   18
         Experts  ......................................................................................   18
         Where You Can Find More Information............................................................   18
         Documents Incorporated by Reference............................................................   19
</TABLE>

                                  ------------

         YOU SHOULD RELY ONLY ON THE INFORMATION CONTAINED IN THIS DOCUMENT OR
TO WHICH WE HAVE REFERRED YOU. NEITHER WE NOR THE SELLING STOCKHOLDERS HAVE
AUTHORIZED ANYONE TO PROVIDE YOU WITH INFORMATION THAT IS DIFFERENT. THIS
DOCUMENT MAY ONLY BE USED WHERE IT IS LEGAL TO SELL THESE SECURITIES. THE
INFORMATION IN THIS DOCUMENT MAY ONLY BE ACCURATE ON THE DATE OF THIS DOCUMENT.

                                  ------------

         In this prospectus, "Lexicon," "we," "us" and "our" refer to Lexicon
Genetics Incorporated.

                                  ------------

         The Lexicon name and logo and OmniBank(R) are registered trademarks and
LexVision(TM) and e-Biology(TM) are trademarks of Lexicon Genetics
Incorporated.
<PAGE>   4
                          LEXICON GENETICS INCORPORATED

         Lexicon Genetics Incorporated is a drug discovery company of the
post-genome era, using gene knockout technology to define the functions of genes
for the discovery of pharmaceutical products. We are using this technology to
expand our LexVision program and fuel drug discovery programs in cancer,
cardiovascular disease, immune disorders, neurological disease, diabetes and
obesity. We have established drug discovery alliances and functional genomics
collaborations with leading pharmaceutical and biotechnology companies, research
institutions and academic institutions throughout the world to commercialize our
technology and further develop our discoveries.

         We generate our gene function discoveries using knockout mice - mice
whose DNA has been altered to disrupt, or "knock out," the function of the
altered gene. Our patented gene trapping and gene targeting technologies enable
us to rapidly generate these knockout mice by altering the DNA of genes in a
special variety of mouse cells, called embryonic stem (ES) cells, which can be
cloned and used to generate mice with the altered gene. We employ an integrated
platform of advanced medical technologies to systematically discover the
functions and potential pharmaceutical uses of the genes we have knocked out. We
believe that our LexVision database, which captures and catalogues the
information resulting from this analysis, and our OmniBank library of more than
150,000 knockout mouse clones provide us and our collaborators significant
opportunities to discover and develop pharmaceutical products based on genomics
- the study of genes and their function.

         In July 2001, we acquired Coelacanth Corporation, a company that uses
proprietary chemistry technologies to rapidly discover new chemical entities for
drug development. Coelacanth forms the core of our new Lexicon Pharmaceuticals
division, combining our novel, functionally defined targets from the human
genome with high performance chemistry technologies to discover new drugs. We
believe the combination of our industrialized in vivo gene function discovery
platform with Coelacanth's established chemistry capability will place us in a
superior position to form drug discovery alliances.

         Lexicon Genetics was incorporated in Delaware in July 1995, and
commenced operations in September 1995. Our corporate headquarters are located
at 4000 Research Forest Drive, The Woodlands, Texas 77381, and our telephone
number is (281) 364-0100. Our corporate website is located at
www.lexicon-genetics.com. Information found on our website should not be
considered part of this prospectus.


                                       3
<PAGE>   5
                                  RISK FACTORS


         You should carefully consider the following risk factors and all other
information contained in this prospectus before purchasing our common stock.
Investing in our common stock involves a high degree of risk. If any of the
following risks actually occurs, we may not be able to conduct our business as
currently planned and our financial condition and operating results could be
seriously harmed. In addition, the trading price of our common stock could
decline due to the occurrence of any of these risks, and you may lose all or
part of your investment. See "Special Note Regarding Forward-Looking
Statements."

RISKS RELATED TO OUR BUSINESS

WE HAVE A HISTORY OF NET LOSSES, AND WE EXPECT TO CONTINUE TO INCUR NET LOSSES
AND MAY NOT ACHIEVE OR MAINTAIN PROFITABILITY

         We have incurred net losses since our inception, including net losses
of approximately $26.0 million for the year ended December 31, 2000 and $17.9
million for the six months ended June 30, 2001. As of June 30, 2001, we had an
accumulated deficit of approximately $72.8 million. We are unsure when we will
become profitable, if ever. The size of our net losses will depend, in part, on
the rate of growth, if any, in our revenues and on the level of our expenses.

         We derive substantially all of our revenues from subscriptions to our
databases, functional genomics collaborations for the development and, in some
cases, analysis of knockout mice, and technology licenses, and will continue to
do so for the foreseeable future. Revenues from database subscriptions,
collaborations and licenses are uncertain because our existing agreements have
fixed terms or relate to specific projects of limited duration. Our ability to
secure future agreements will depend upon our ability to address the needs of
our potential future subscribers and collaborators.

         A large portion of our expenses are fixed, including expenses related
to facilities, equipment and personnel. In addition, we expect to spend
significant amounts to fund research and development and to enhance our core
technologies. As a result, we expect that our operating expenses will increase
significantly in the near term and, consequently, we will need to generate
significant additional revenues to achieve profitability. Even if we do achieve
profitability, we may not be able to sustain or increase profitability on a
quarterly or annual basis.

OUR QUARTERLY OPERATING RESULTS HAVE BEEN AND LIKELY WILL CONTINUE TO FLUCTUATE,
AND WE BELIEVE THAT QUARTER-TO-QUARTER COMPARISONS OF OUR OPERATING RESULTS ARE
NOT A GOOD INDICATION OF OUR FUTURE PERFORMANCE

         Our quarterly operating results have fluctuated in the past and are
likely to do so in the future. In addition to the risks and uncertainties
described in this section, some of the factors that could cause our operating
results to fluctuate include:

     -    our ability to establish new database subscriptions or research
          contracts with collaborators and new technology licenses, and the
          timing of such arrangements;

     -    the expiration or other termination of database subscriptions or
          research contracts with our collaborators or technology licenses,
          which may not be renewed or replaced;

     -    the success rate of our discovery efforts leading to milestone
          payments and royalties;

     -    the timing and willingness of our collaborators to commercialize
          pharmaceutical products which would result in milestone payments and
          royalties; and

     -    general and industry-specific economic conditions, which may affect
          our and our collaborators' research and development expenditures.

         Due to the likelihood of fluctuations in our revenues and expenses, we
believe that quarter-to-quarter comparisons of our operating results are not a
good indication of our future performance. Our operating results in


                                       4
<PAGE>   6
some quarters may not meet the expectations of stock market analysts and
investors. In that case, our stock price would probably decline.

WE ARE AN EARLY-STAGE COMPANY WITH AN UNPROVEN BUSINESS STRATEGY

         Our business strategy of using our gene sequence databases and knockout
mice to select promising candidates for drug target development and
commercializing our discoveries through collaborations and alliances is
unproven. Our success will depend upon our ability to enter into additional
collaboration and alliance agreements on favorable terms, determine which genes
have potential value and select an appropriate commercialization strategy for
each potential product we or our collaborators choose to pursue.

         Biotechnology and pharmaceutical companies have successfully developed
and commercialized only a limited number of gene-based pharmaceutical products
to date. We have not proven our ability to identify gene-based drugs or drug
targets with commercial potential, or to develop or commercialize drugs or drug
targets that we do identify. It is difficult to successfully select those genes
with the most potential for commercial development, and we do not know that any
pharmaceutical products based on genes that we discover can be successfully
commercialized. In addition, we may experience unforeseen technical
complications in the processes we use to generate our gene sequence database and
functional genomics resources. These complications could materially delay or
limit the use of those databases and resources, substantially increase the
anticipated cost of generating them or prevent us from implementing our
processes at appropriate quality and throughput levels.

WE FACE SUBSTANTIAL COMPETITION IN THE DISCOVERY OF THE DNA SEQUENCES OF GENES
AND THEIR FUNCTIONS AND IN OUR DRUG DISCOVERY AND PRODUCT DEVELOPMENT EFFORTS

         There are a finite number of genes in the human genome, and we believe
that the majority of such genes have been identified by us or others conducting
genomic research and that virtually all will be identified within the next few
years. We face significant competition in our efforts to discover and patent the
sequence and other information derived from such genes from entities using
alternative, and in some cases higher volume and larger scale, approaches for
the same purpose.

         We also face competition from entities using more traditional methods
to discover genes related to particular diseases. Many of these entities have
substantially greater financial, scientific and human resources than we do. A
large number of universities and other not-for-profit institutions, many of
which are funded by the U.S. and foreign governments, are also conducting
research to discover genes. A substantial portion of this research has been
conducted under the international Human Genome Project, a multi-billion dollar
program funded by the U.S. government and The Wellcome Trust. One or more of
these entities may discover and establish a patent position in one or more of
the genes that we wish to study or use in the development of a pharmaceutical
product.

         We face significant competition in our drug discovery and product
development efforts from entities using traditional knockout mouse technology
and other functional genomics technologies, as well as from those using other
traditional drug discovery techniques. These competitors may develop products
earlier than we do, obtain regulatory approvals faster than we can and develop
products that are more effective than ours. Our ability to use our patent rights
to prevent competition in the creation and use of knockout mice is more limited
outside of the United States. Competitors could discover and establish patents
in genes or gene products that we or our collaborators identify as a drug target
or therapeutic protein. Numerous companies, academic institutions and government
consortia are engaged in efforts to determine the function of genes and gene
products. Furthermore, other methods for conducting functional genomics research
may ultimately prove superior, in some or all respects, to the use of knockout
mice. In addition, technologies more advanced than or superior to our gene
trapping technology may be developed, thereby rendering our gene trapping
technology obsolete.

WE RELY HEAVILY ON COLLABORATORS TO DEVELOP AND COMMERCIALIZE PHARMACEUTICAL
PRODUCTS BASED ON GENES THAT WE IDENTIFY AS PROMISING CANDIDATES FOR DEVELOPMENT
AS DRUG TARGETS

         Since we do not currently possess the resources necessary to develop,
obtain approvals for or commercialize potential pharmaceutical products based on
genes contained in our databases or genes that we identify as promising
candidates for development as drug targets or therapeutic proteins, we must
enter into


                                       5
<PAGE>   7
collaborative arrangements to develop and commercialize these products. We will
have limited or no control over the resources that any collaborator may devote
to this effort. Any of our present or future collaborators may not perform their
obligations as expected. These collaborators may breach or terminate their
agreements with us or otherwise fail to conduct product discovery, development
or commercialization activities successfully or in a timely manner. Further, our
collaborators may elect not to develop pharmaceutical products arising out of
our collaborative arrangements or may not devote sufficient resources to the
development, approval, manufacture, marketing or sale of these products. If any
of these events occurs, we may not be able to develop or commercialize potential
pharmaceutical products.

         Some of our agreements provide us with rights to participate in the
commercial development of compounds or therapeutic approaches derived from our
collaborations or access to our databases, technology or intellectual property.
We may not be able to obtain such rights in future collaborations or agreements.
Our ability to obtain such rights depends in part on the validity of our
intellectual property, the advantages and novelty of our technologies and
databases and our negotiating position relative to each potential collaborator
or customer. Previous attempts by others in the industry to obtain these rights
with respect to the development of knockout mice and related technologies have
generated considerable controversy, especially in the academic community.

ANY CANCELLATION BY OR CONFLICTS WITH OUR COLLABORATORS COULD HARM OUR BUSINESS

         Our collaboration agreements may not be renewed and may be terminated
in the event either party fails to fulfill its obligations under these
agreements. Any failure to renew or cancellation by a collaborator could mean a
significant loss of revenues and volatility in our earnings.

         In addition, we may pursue opportunities in fields that could conflict
with those of our collaborators. Moreover, disagreements could arise with our
collaborators over rights to our intellectual property or our rights to share in
any of the future revenues of compounds or therapeutic approaches developed by
our collaborators. These kinds of disagreements could result in costly and
time-consuming litigation. Any conflict with our collaborators could reduce our
ability to obtain future collaboration agreements and could have a negative
impact on our relationship with existing collaborators, adversely affecting our
business and revenues. Some of our collaborators could also become competitors
in the future. Our collaborators could develop competing products, preclude us
from entering into collaborations with their competitors or terminate their
agreements with us prematurely. Any of these developments could harm our product
development efforts.

WE HAVE NO EXPERIENCE IN DEVELOPING AND COMMERCIALIZING PHARMACEUTICAL PRODUCTS
ON OUR OWN

         Our ability to develop and commercialize pharmaceutical products on our
own will depend on our ability to internally develop preclinical, clinical,
regulatory and sales and marketing capabilities, or enter into arrangements with
third parties to provide those functions. We may not be successful in developing
these capabilities or entering into agreements with third parties on favorable
terms, or at all. Further, our reliance upon third parties for these
capabilities could reduce our control over such activities and could make us
dependent upon these parties. Our inability to develop or contract for these
capabilities would significantly impair our ability to develop and commercialize
pharmaceutical products.

WE MAY ENGAGE IN FUTURE ACQUISITIONS, WHICH MAY BE EXPENSIVE AND TIME CONSUMING
AND FROM WHICH WE MAY NOT REALIZE ANTICIPATED BENEFITS

         We may acquire additional businesses, technologies and products, if we
determine that these businesses, technologies and products complement our
existing technology or otherwise serve our strategic goals. We currently have no
commitments or agreements with respect to any acquisitions. If we do undertake
any transactions of this sort, the process of integrating an acquired business,
technology or product may result in operating difficulties and expenditures and
may absorb significant management attention that would otherwise be available
for ongoing development of our business. Moreover, we may never realize the
anticipated benefits of any acquisition. Future acquisitions could result in
potentially dilutive issuances of our equity securities, the incurrence of debt
and contingent liabilities and amortization expenses related to goodwill and
other intangible assets, which could adversely affect our results of operations
and financial condition.


                                       6
<PAGE>   8
IF WE LOSE OUR KEY PERSONNEL OR ARE UNABLE TO ATTRACT AND RETAIN ADDITIONAL
PERSONNEL, WE MAY BE UNABLE TO PURSUE COLLABORATIONS OR DEVELOP OUR OWN PRODUCTS

         We are highly dependent on Arthur T. Sands, M.D., Ph.D., our president
and chief executive officer, as well as other principal members of our
management and scientific staff. The loss of any of these personnel would have a
material adverse effect on our business, financial condition or results of
operations and could inhibit our product development and commercialization
efforts. Although we have entered into employment agreements with some of our
key personnel, including Dr. Sands, these employment agreements are for a
limited period of time and not all key personnel have employment agreements.

         Recruiting and retaining qualified scientific personnel to perform
future research and development work will be critical to our success.
Competition for experienced scientists is high. Failure to recruit and retain
scientific personnel on acceptable terms could prevent us from achieving our
business objectives.

WE MAY ENCOUNTER DIFFICULTIES IN MANAGING OUR GROWTH, WHICH COULD INCREASE OUR
LOSSES

         We have experienced a period of rapid growth that has placed and, if
this growth continues, will continue to place a strain on our human and capital
resources. If we are unable to manage our growth effectively, our losses could
increase. The number of our employees increased from 57 at December 31, 1997 to
93 at December 31, 1998, 122 at December 31, 1999, 287 at December 31, 2000 and
371 at June 30, 2001. We intend to increase the number of our employees
significantly during the remainder of 2001. Our ability to manage our operations
and growth effectively requires us to continue to expend funds to improve our
operational, financial and management controls, reporting systems and
procedures. If we are unable to successfully implement improvements to our
management information and control systems in an efficient or timely manner, or
if we encounter deficiencies in existing systems and controls, our management
may not have adequate information to manage our day-to-day operations.

BECAUSE OUR ENTIRE OMNIBANK MOUSE CLONE LIBRARY IS LOCATED AT A SINGLE FACILITY,
THE OCCURRENCE OF A DISASTER COULD SIGNIFICANTLY DISRUPT OUR BUSINESS

         Our OmniBank mouse clone library and its back-up are stored in liquid
nitrogen freezers located at our facility in The Woodlands, Texas. If a disaster
such as a fire, flood, hurricane, tornado or similar event significantly damages
or destroys the facility in which our mouse clone library and back-up are
stored, our business could be disrupted until we could regenerate the library
and, as a result, our stock price could decline. Our business interruption
insurance may not be sufficient to compensate us in the event of a major
interruption due to such a disaster.

WE MAY NEED ADDITIONAL CAPITAL IN THE FUTURE AND, IF IT IS NOT AVAILABLE, WE
WILL HAVE TO CURTAIL OR CEASE OPERATIONS

         Our future capital requirements will be substantial and will depend on
many factors, including our ability to obtain database subscription and
collaboration agreements and government grants, the amount and timing of
payments under such agreements and grants, the level and timing of our research
and development expenditures, market acceptance of our products, the resources
we devote to developing and supporting our products and other factors. Our
capital requirements will also be affected by any expenditures we make in
connection with license agreements and acquisitions of and investments in
complementary technologies and businesses.

         We anticipate that our existing capital resources will enable us to
maintain our currently planned operations for at least the next several years.
However, changes may occur that would consume available capital resources
significantly sooner than we expect. If our capital resources are insufficient
to meet future capital requirements, we will have to raise additional funds to
continue the development of our technologies and complete the commercialization
of products, if any, resulting from our technologies. We may be unable to raise
sufficient additional capital; if so, we will have to curtail or cease
operations.


                                       7
<PAGE>   9
RISKS RELATED TO OUR INDUSTRY

OUR ABILITY TO PATENT OUR DISCOVERIES IS UNCERTAIN BECAUSE PATENT LAWS AND THEIR
INTERPRETATION ARE HIGHLY UNCERTAIN AND SUBJECT TO CHANGE

         The patent positions of biotechnology firms generally are highly
uncertain and involve complex legal and factual questions that will determine
who has the right to develop a particular product. No clear policy has emerged
regarding the breadth of claims covered in biotechnology patents. The
biotechnology patent situation outside the United States is even more uncertain
and is currently undergoing review and revision in many countries. Changes in,
or different interpretations of, patent laws in the United States and other
countries might allow others to use our discoveries or to develop and
commercialize our products without any compensation to us. We anticipate that
these uncertainties will continue for a significant period of time.

OUR PATENT APPLICATIONS MAY NOT RESULT IN ENFORCEABLE PATENT RIGHTS

         Our disclosures in our patent applications may not be sufficient to
meet the statutory requirements for patentability. Additionally, our current
patent applications cover many genes and we expect to file patent applications
in the future covering many more genes. As a result, we cannot predict which of
our patent applications will result in the granting of patents or the timing of
the granting of our patents. Our ability to obtain patent protection based on
genes or partial gene sequences will depend, in part, upon identification of a
function for the gene or gene sequences sufficient to meet the statutory
requirement that an invention have utility and that a patent application
describe the invention with sufficient specificity. While the U.S. Patent and
Trademark Office has issued guidelines for the examination of patent
applications claiming gene sequences, their therapeutic uses and novel proteins
coded by such genes, the impact of these guidelines is uncertain and may delay
or negatively impact our patent position. Biologic data in addition to that
obtained by our current technologies may be required for issuance of patents or
human therapeutics. If required, obtaining such biologic data could delay, add
substantial costs to, or affect our ability to obtain patent protection. There
can be no assurance that the disclosures in our current or future patent
applications, including those we may file with our collaborators, will be
sufficient to meet these requirements. Alternatively, if the level of biologic
or other experimental data required to obtain a patent is determined to be
minimal, then other companies who emphasize determining the gene sequence
without significant biologic function information will obtain a prior and
superior patent position to us and our collaborators. Even if patents are
issued, there may be current or future uncertainty as to the scope of the
coverage or protection provided by any such patents. In addition, the Human
Genome Project, as well as many companies and institutions, have identified
genes and deposited partial gene sequences in public databases and are
continuing to do so. These public disclosures might limit the scope of our
claims or make unpatentable subsequent patent applications on full-length genes.

         Other companies or institutions have filed and will file patent
applications that attempt to patent genes or gene sequences that may be similar
to our patent applications. The U.S. Patent and Trademark Office could decide
competing patent claims in an interference proceeding. Any such proceeding would
be costly, and we may not prevail. In addition, patent applications filed by
third parties may have priority over patent applications we file. In this event,
the prevailing party may require us or our collaborators to stop pursuing a
potential product or to negotiate a license arrangement to pursue the potential
product. We may not be able to obtain a license from the prevailing party on
acceptable terms, or at all.

         Some court decisions indicate that disclosure of a partial sequence may
not be sufficient to support the patentability of a full-length sequence. These
decisions have been confirmed by recent pronouncements of the U.S. Patent and
Trademark Office. We believe that these court decisions and the uncertain
position of the U.S. Patent and Trademark Office present a significant risk that
the U.S. Patent and Trademark Office will not issue patents based on patent
disclosures limited to partial gene sequences, like those represented in our
human gene trap database. In addition, we are uncertain about the scope of the
coverage, enforceability and commercial protection provided by any patents
issued on the basis of partial gene sequences.


                                       8
<PAGE>   10
IF OTHER COMPANIES AND INSTITUTIONS OBTAIN PATENTS CLAIMING THE FUNCTIONAL USES
OF GENES AND GENE PRODUCTS BASED UPON GENE SEQUENCE INFORMATION AND PREDICTIONS
OF GENE FUNCTION, WE MAY BE UNABLE TO OBTAIN PATENTS FOR OUR DISCOVERIES OF
BIOLOGICAL FUNCTIONS IN KNOCKOUT MICE

         We intend to pursue patent protection covering the novel uses and
functions of new and known genes and proteins in mammalian physiology and
disease states. While an actual description of the biological function of a gene
or protein should enhance a patent position, we cannot assure you that such
information will increase the probability of issuance of any patents. Further,
many other entities are currently filing patents on genes which are identical or
similar to our filings. Many such applications seek to protect partial human
gene sequences, full-length gene sequences and the deduced protein products
encoded by the sequences while others use biological or other laboratory data.
Some of these applications attempt to assign biologic function to the DNA
sequences based on computer predictions. There is the significant possibility
that patents claiming the functional uses of genes and gene products will be
issued to our competitors based on such information.

WE ARE PRESENTLY INVOLVED IN PATENT LITIGATION AND MAY BE INVOLVED IN FUTURE
PATENT LITIGATION AND OTHER DISPUTES REGARDING INTELLECTUAL PROPERTY RIGHTS, AND
CAN GIVE NO ASSURANCES THAT WE WILL PREVAIL IN ANY SUCH LITIGATION OR OTHER
DISPUTE

         Our potential products and those of our collaborators may give rise to
claims that they infringe the patents of others. This risk will increase as the
biotechnology industry expands and as other companies obtain more patents and
attempt to discover genes through the use of high-speed sequencers. In addition,
many companies have well-established patent portfolios directed to common
techniques, methods and means of developing, producing and manufacturing
pharmaceutical products. Other companies or institutions could bring legal
actions against us or our collaborators for damages or to stop us or our
collaborators from manufacturing and marketing the affected products. If any of
these actions are successful, in addition to our potential liability for
damages, these entities may require us or our collaborators to obtain a license
in order to continue to manufacture or market the affected products or may force
us to terminate manufacturing or marketing efforts.

         We may need to pursue litigation against others to enforce our patents
and intellectual property rights. Patent litigation is expensive and requires
substantial amounts of management attention. In addition, the eventual outcome
of any such litigation is uncertain.

         On May 24, 2000, we filed a complaint against Deltagen, Inc. in U.S.
District Court for the District of Delaware alleging that Deltagen is willfully
infringing the claims of United States Patent No. 5,789,215, under which we hold
an exclusive license from GenPharm International, Inc. This patent covers
methods of engineering the animal genome, including methods for the production
of knockout mice by homologous recombination, using isogenic DNA technology. In
the complaint, we are seeking unspecified damages from Deltagen, as well as
injunctive relief. Deltagen has counterclaimed for a declaratory judgment that
the patent is invalid and unenforceable and is not infringed by Deltagen. On
November 14, 2000, Deltagen filed an amended counterclaim alleging antitrust
claims against us and GenPharm, for which Deltagen is seeking unspecified
damages.

         On October 13, 2000, we filed a second complaint against Deltagen, Inc.
in U.S. District Court for the Northern District of California alleging that
Deltagen is willfully infringing the claims of United States Patents Nos.
5,464,764, 5,487,992, 5,627,059, and 5,631,153, under which also we hold
exclusive licenses from GenPharm International. These patents cover methods and
vectors for using positive-negative selection for producing gene targeted, or
"knockout," cells and animals, including the production of knockout mice by
homologous recombination. In the complaint, we are seeking unspecified damages
from Deltagen, as well as injunctive relief. Deltagen has counterclaimed for a
declaratory judgment that the patents are invalid and unenforceable and are not
infringed by Deltagen.

         While we believe that our complaints against Deltagen are meritorious
and that Deltagen's counterclaims against us are without merit, we can provide
no assurance that we will prevail in our litigation against Deltagen or that, if
we prevail, any damages or equitable remedies awarded will be commercially
valuable. If Deltagen prevails in declaring our patents invalid or on its
antitrust claim against us, our business and financial position could be
adversely affected. Furthermore, we are likely to incur substantial costs and
expend substantial personnel time in pursuing our litigation against Deltagen.



                                       9
<PAGE>   11
         We believe that there will continue to be significant litigation in our
industry regarding patent and other intellectual property rights. We and many of
our competitors have and are continuing to expend significant amounts of time,
money and management resources on intellectual property litigation. If we become
involved in additional litigation, it could consume a substantial portion of our
resources and could negatively affect our results of operations.

         Patent litigation involves substantial risks. Each time we sue for
patent infringement we face the risk that the patent will be held invalid or
unenforceable. Such a determination is binding on us for all future litigation
involving that patent. Furthermore, in light of recent U.S. Supreme Court
precedent, our ability to enforce our patents against state agencies, including
state sponsored universities and research labs is limited by the Eleventh
Amendment to the U.S. Constitution. Finally, opposition by academicians and the
government may hamper our ability to enforce our patent against academic or
government research laboratories. Enforcement of our patents may cause our
reputation in the academic community to be injured.

ISSUED PATENTS MAY NOT FULLY PROTECT OUR DISCOVERIES, AND OUR COMPETITORS MAY BE
ABLE TO COMMERCIALIZE PRODUCTS SIMILAR TO THOSE COVERED BY OUR ISSUED PATENTS

         Issued patents may not provide commercially-meaningful protection
against competitors. Other companies or institutions may challenge our or our
collaborators' patents or independently develop similar products that could
result in an interference proceeding in the Patent and Trademark Office or a
legal action. In the event any single researcher or institution infringes upon
our or our collaborators' patent rights, enforcing these rights may be difficult
and time consuming. Others may be able to design around these patents or develop
unique products providing effects similar to our products. We may be required to
choose between pursuing litigation against infringers and being unable to
recover damages or otherwise enforce our patent rights.

         In addition, others may discover uses for genes or proteins other than
those uses covered in our patents, and these other uses may be separately
patentable. Even if we have a patent claim on a particular gene, the holder of a
patent covering the use of that gene could exclude us from selling a product
that is based on the same use of that gene. In addition, with respect to certain
of our patentable inventions, we have decided not to pursue patent protection
outside the United States, both because we do not believe it is cost effective
and because of confidentiality concerns. Accordingly, our international
competitors could develop, and receive foreign patent protection for gene
sequences and functions for which we are seeking U.S. patent protection.

OUR RIGHTS TO THE USE OF TECHNOLOGIES LICENSED BY THIRD PARTIES ARE NOT WITHIN
OUR CONTROL

         We rely, in part, on licenses to use certain technologies that are
material to our business. We do not own the patents that underlie these
licenses. Our rights to use these technologies and practice the inventions
claimed in the licensed patents are subject to our licensors abiding by the
terms of those licenses and not terminating them. In many cases, we do not
control the prosecution or filing of the patents to which we hold licenses. We
rely upon our licensors to prevent infringement of those patents. The scope of
our rights under our licenses may be subject to dispute by our licensors or
third parties.

WE MAY BE UNABLE TO PROTECT OUR TRADE SECRETS

         While we have entered into confidentiality agreements with employees
and collaborators, we may not be able to prevent the disclosure of our trade
secrets. In addition, other companies or institutions may independently develop
substantially equivalent information and techniques.

WE MAY BECOME SUBJECT TO REGULATION UNDER THE ANIMAL WELFARE ACT, WHICH COULD
SUBJECT US TO ADDITIONAL COSTS AND PERMIT REQUIREMENTS

         The Animal Welfare Act, or AWA, is the federal law that currently
covers animals in laboratories. It applies to institutions or facilities using
any regulated live animals for research, testing, teaching or experimentation,
including diagnostic laboratories and private companies in the pharmaceutical
and biotechnology industries. The AWA currently does not cover rats or mice.
However, the United States Department of Agriculture, which enforces


                                       10
<PAGE>   12
the AWA, has entered into a proposed settlement agreement under which it has
agreed to commence the process of adopting regulations under the AWA to include
mice within its coverage.

         Currently, the AWA imposes a wide variety of specific regulations which
govern the humane handling, care, treatment and transportation of certain
animals by producers and users of research animals, most notably personnel,
facilities, sanitation, cage size, feeding, watering and shipping conditions. If
the USDA includes mice in its regulations, we will become subject to
registration, inspections and reporting requirements. Compliance with the AWA
could be expensive, and the regulations eventually adopted by the USDA could
impair our research and production efforts.

WE AND OUR COLLABORATORS ARE SUBJECT TO EXTENSIVE AND UNCERTAIN GOVERNMENT
REGULATORY REQUIREMENTS, WHICH COULD INCREASE OUR OPERATING COSTS OR ADVERSELY
AFFECT OUR ABILITY TO OBTAIN GOVERNMENT APPROVAL OF PRODUCTS BASED ON GENES THAT
WE IDENTIFY IN A TIMELY MANNER OR AT ALL

         Since we develop animals containing changes in their genetic make-up,
we may become subject to a variety of laws, guidelines, regulations and treaties
specifically directed at genetically modified organisms, or GMOs. The area of
environmental releases of GMOs is rapidly evolving and is currently subject to
intense regulatory scrutiny, particularly internationally. If we become subject
to these laws we could incur substantial compliance costs. For example, the
Biosafety Protocol, or the BSP, a recently adopted treaty, is expected to cover
certain shipments from the United States to countries abroad that have signed
the BSP. The BSP is also expected to cover the importation of living modified
organisms, a category that could include our animals. If our animals are not
contained as described in the BSP, our animals could be subject to the
potentially extensive import requirements of countries that are signatories to
the BSP.

         Drugs and diagnostic products are subject to an extensive and uncertain
regulatory approval process by the FDA and comparable agencies in other
countries. The regulation of new products is extensive, and the required process
of laboratory testing and human studies is lengthy and expensive. The burden of
these regulations will fall on us to the extent we develop proprietary products
on our own. If the products are the result of a collaboration effort, these
burdens may fall on our collaborating partner or may be shared with us. We may
not be able to obtain FDA approvals for those products in a timely manner, or at
all. We may encounter significant delays or excessive costs in our efforts to
secure necessary approvals or licenses. Even if we obtain FDA regulatory
approvals, the FDA extensively regulates manufacturing, labeling, distributing,
marketing, promotion and advertising after product approval. Moreover, several
of our product development areas may involve relatively new technology and have
not been the subject of extensive product testing in humans. The regulatory
requirements governing these products and related clinical procedures remain
uncertain and the products themselves may be subject to substantial review by
foreign governmental regulatory authorities that could prevent or delay approval
in those countries. Regulatory requirements ultimately imposed on our products
could limit our ability to test, manufacture and, ultimately, commercialize our
products.

SECURITY RISKS IN ELECTRONIC COMMERCE OR UNFAVORABLE INTERNET REGULATION MAY
DETER FUTURE USE OF OUR PRODUCTS AND SERVICES

         We provide access to our databases and the opportunity to acquire our
knockout mice on the Internet. A fundamental requirement to conduct
Internet-based electronic commerce is the secure transmission of confidential
information over public networks. Advances in computer capabilities, new
discoveries in the field of cryptography or other developments may result in a
compromise or breach of the algorithms we use to protect content and
transactions on Lexgen.com or proprietary information in our OmniBank database.
Anyone who is able to circumvent our security measures could misappropriate our
proprietary information, confidential customer information or cause
interruptions in our operations. We may be required to incur significant costs
to protect against security breaches or to alleviate problems caused by
breaches. Further, a well-publicized compromise of security could deter people
from using the Internet to conduct transactions that involve transmitting
confidential information.

         Because of the growth in electronic commerce, Congress has held
hearings on whether to regulate providers of services and transactions in the
electronic commerce market, and federal or state authorities could enact laws,
rules or regulations affecting our business or operations. If enacted and
applied to our business, these laws, rules or regulations could render our
business or operations more costly, burdensome, less efficient or impracticable.


                                       11
<PAGE>   13
WE USE HAZARDOUS CHEMICALS AND RADIOACTIVE AND BIOLOGICAL MATERIALS IN OUR
BUSINESS; ANY DISPUTES RELATING TO IMPROPER HANDLING, STORAGE OR DISPOSAL OF
THESE MATERIALS COULD BE TIME CONSUMING AND COSTLY

         Our research and development processes involve the use of hazardous
materials, including chemicals and radioactive and biological materials. Our
operations also produce hazardous waste products. We cannot eliminate the risk
of accidental contamination or discharge or any resultant injury from these
materials. Federal, state and local laws and regulations govern the use,
manufacture, storage, handling and disposal of these materials. We could be
subject to civil damages in the event of an improper or unauthorized release of,
or exposure of individuals to, these hazardous materials. In addition, claimants
may sue us for injury or contamination that results from our use or the use by
third parties of these materials, and our liability may exceed our total assets.
Compliance with environmental laws and regulations may be expensive, and current
or future environmental regulations may impair our research, development or
production efforts.

WE MAY BE SUED FOR PRODUCT LIABILITY

         We or our collaborators may be held liable if any product we or our
collaborators develop, or any product which is made with the use or
incorporation of any of our technologies, causes injury or is found otherwise
unsuitable during product testing, manufacturing, marketing or sale. Although we
currently have and intend to maintain product liability insurance, this
insurance may become prohibitively expensive, or may not fully cover our
potential liabilities. Inability to obtain sufficient insurance coverage at an
acceptable cost or otherwise to protect against potential product liability
claims could prevent or inhibit the commercialization of products developed by
us or our collaborators. If we are sued for any injury caused by our or our
collaborators' products, our liability could exceed our total assets.

PUBLIC PERCEPTION OF ETHICAL AND SOCIAL ISSUES MAY LIMIT OR DISCOURAGE THE USE
OF OUR TECHNOLOGIES, WHICH COULD REDUCE OUR REVENUES

         Our success will depend in part upon our ability to develop products
discovered through our gene trapping and knockout mouse technologies.
Governmental authorities could, for ethical, social or other purposes, limit the
use of genetic processes or prohibit the practice of our gene trapping and
knockout mouse technologies. Claims that genetically engineered products are
unsafe for consumption or pose a danger to the environment may influence public
perceptions. The subject of genetically modified organisms, like knockout mice,
has received negative publicity and aroused public debate in some countries.
Ethical and other concerns about our technologies, particularly the use of genes
from nature for commercial purposes and the products resulting from this use,
could adversely affect the market acceptance of our technologies.

RISKS RELATED TO THIS OFFERING

OUR STOCK PRICE HAS BEEN AND LIKELY WILL CONTINUE TO BE VOLATILE, AND YOUR
INVESTMENT MAY SUFFER A DECLINE IN VALUE

         The stock market has experienced significant price and volume
fluctuations, and the market prices of technology companies, particularly
biotechnology companies such as ours, have been highly volatile. In addition,
broad market and industry fluctuations that are not within our control may
adversely affect the trading price of our common stock. You may not be able to
sell your shares at or above your purchase price.

PROVISIONS OF OUR CHARTER DOCUMENTS AND DELAWARE LAW MAY INHIBIT A TAKEOVER,
WHICH COULD NEGATIVELY AFFECT OUR STOCK PRICE

         Provisions in our amended and restated charter and bylaws and
applicable provisions of the Delaware General Corporation Law may make it more
difficult for a third party to acquire control of us without the approval of our
board of directors. These provisions may make it more difficult or expensive for
a third party to acquire a majority of our outstanding voting common stock or
delay, prevent or deter a merger, acquisition, tender offer or proxy contest,
which may negatively affect our stock price.



                                       12
<PAGE>   14
                SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

         This prospectus contains forward-looking statements. These statements
relate to future events or our future financial performance. We have attempted
to identify forward-looking statements by terminology including "anticipate,"
"believe," "can," "continue," "could," "estimate," "expect," "intend," "may,"
"plan," "potential," "predict," "should" or "will" or the negative of these
terms or other comparable terminology. These statements are only predictions and
involve known and unknown risks, uncertainties and other factors, including the
risks outlined under "Risk Factors," that may cause our or our industry's actual
results, levels of activity, performance or achievements to be materially
different from any future results, levels or activity, performance or
achievements expressed or implied by these forward-looking statements.

         Although we believe that the expectations reflected in the
forward-looking statements are reasonable, we cannot guarantee future results,
levels of activity, performance or achievements. We are not under any duty to
update any of the forward-looking statements after the date of this prospectus
to conform these statements to actual results, unless required by law.

                                 USE OF PROCEEDS

         All of the shares offered by this prospectus are being offered and sold
by the selling stockholders. We will not receive any proceeds from the sale of
the shares of common stock offered by the selling stockholders.

         The selling stockholders will pay any underwriting discounts and
commissions, brokerage fees and other expenses, including fees and expenses of
counsel, which they incur in selling shares of our common stock. We will pay all
expenses for the registration of the selling stockholders' offer and sale of the
shares of common stock covered by this prospectus, including registration fees
and the costs and expenses of our counsel and independent public accountants.

                              SELLING STOCKHOLDERS

         We issued the shares of common stock covered by this prospectus:

         -        in connection with our acquisition of the outstanding
                  securities of Coelacanth Corporation in a merger completed on
                  July 12, 2001; and

         -        in private placements completed prior to our April 2000
                  initial public offering.

         In connection with the Coelacanth merger, we agreed to register the
resale of the shares of common stock received in the merger by Coelacanth's
former stockholders and to use our commercially reasonable best efforts to keep
the registration statement effective for 24 months or, if earlier, until all of
the common stock received in the merger may be sold by the selling stockholders
under Rule 144 under the Securities Act of 1933 in a 90-day period. The other
selling stockholders requested that we register their resale of shares of common
stock under a registration rights agreement in which we agreed to use
commercially reasonable best efforts to include their shares in a registration
in which they request to participate. All of the shares offered by the selling
stockholders were issued in transactions exempt from the registration
requirements of the Securities Act of 1933.

         The selling stockholders, or their donees of 500 or fewer shares, may
offer the shares of common stock covered by this prospectus from time to time.
Our registration of the selling stockholders' resale of such shares does not
necessarily mean that the selling stockholders will sell any or all of their
shares. We do not know when or in what amounts a selling stockholder may offer
shares for sale. Because the selling stockholder may offer all or some of the
shares pursuant to this offering, and because there are currently no agreements,
arrangements or understandings with respect to the sale of any of the shares, we
cannot estimate the number of the shares that will be held by the selling
stockholder after completion of the offering.

         If a selling stockholder transfers more than 500 shares of common stock
by gift, pledge or other non-sale transfer after the effective date of the
registration statement of which this prospectus is a part, the donee, pledgee or


                                       13
<PAGE>   15
transferee may make no offer or sale under this prospectus unless and until a
supplement to this prospectus has been filed or an amendment to the related
registration statement has become effective.

         The table below sets forth the beneficial ownership of all common stock
of each selling stockholder as of July 31, 2001 as well as the number of such
shares of common stock offered by this prospectus. For purposes of determining
the number of shares beneficially owned by a person and the percentage ownership
of that person in accordance with the rules of the SEC, shares of common stock
underlying options held by that person that are currently exercisable or
exercisable within 60 days of July 31, 2001 are considered outstanding. These
shares, however, are not considered outstanding when computing the percentage
ownership of each other person.

         Except as indicated in the footnotes to this table and pursuant to
state community property laws, to our knowledge, each selling stockholder named
in the table has sole voting and investment power for the shares shown as
beneficially owned by them. Percentage of ownership is based on 51,848,452
shares of common stock outstanding on July 31, 2001.

         We prepared this table based on information supplied to us by the
selling stockholders named in the table, and we have not sought to independently
verify such information.

<TABLE>
<CAPTION>
                                                                 BENEFICIAL OWNERSHIP
                                                                  PRIOR TO OFFERING
                                                                  -----------------
                                                                        SHARES
                                                                       ISSUABLE
                                                                      PURSUANT TO
                                                                        OPTIONS
                                                      NUMBER OF       EXERCISABLE
                                                       SHARES          WITHIN 60                         SHARES
                                                     BENEFICIALLY    DAYS OF JULY      PERCENTAGE       OFFERED
          NAME OF SELLING STOCKHOLDER                   OWNED          31, 2001        OWNERSHIP         HEREBY
          ---------------------------                   -----          --------        ---------         ------

Former Coelacanth Stockholders (1)
----------------------------------
<S>                                                  <C>             <C>               <C>              <C>
Brett R. Bosley                                              202                --              *              202
David Brook                                                  202                --              *              202
Eran Broshy                                                7,577                --              *            7,577
California Institute of Technology                           243                --              *              243
Cullen Cavallaro                                             128                --              *              128
Zheng ming Chen                                              131                --              *              131
Jay Chiang                                                 1,429                --              *            1,429
Evangeline Priya Eddy                                        439                --              *              439
Keith Elliston                                                57                --              *               57
Yoany Gervacio                                                27                --              *               27
Seth L. Harrison (2)                                      35,538                --              *           35,538
Hartmuth Kolb (3)                                            810            25,906              *              810
Laxma Reddy Kolla                                            157                --              *              157
Amit Kumar                                                    75                --              *               75
Hanghui Liu                                                  273                --              *              273
Dat Nguyen                                                    18                --              *               18
Denise Prince                                                 30                --              *               30
Vasazi Reddy                                                  60                --              *               60
Michael Richards                                             143                --              *              143
Janice Rothman                                               188                --              *              188
K. Barry and Janet Dueser Sharpless (4)                   72,723                --              *           72,723
John A. Skolas                                             2,702                --              *            2,702
James Wan                                                     37                --              *               37
Jeffrey Whitney                                              158                --              *              158
Barry Wolitzky                                             6,166                --              *            6,166
Daniel J. Bader                                            2,017                --              *            2,017
</TABLE>



                                       14
<PAGE>   16
<TABLE>
<S>                                                      <C>                <C>                 <C>         <C>
Alfred Bader                                              22,524                --              *           22,524
David Bader                                                2,017                --              *            2,017
Robert A. and Ellen F. Bildersee                          10,420                --              *           10,420
Robert L. and Joyce Y. Blumberg                            1,615                --              *            1,615
Robert L. Blumberg                                           402                --              *              402
David A. Boulton (5)                                      20,463            14,681              *           20,463
David Boulton as Custodian for Sarah Boulton (5)             428                --              *              428
Peter B. and Cynthia H. Ellis                             15,700                --              *           15,700
Sally Elson                                                1,011                --              *            1,011
George Fesus                                              15,700                --              *           15,700
Juliet V. Gauchat                                         18,928                --              *           18,928
Edward M. Giles                                            4,046                --              *            4,046
Robert H. and Helen O. Grubbs                              4,289                --              *            4,289
Laura Harrison                                             1,352                --              *            1,352
Alvan Harrison                                               933                --              *              933
Jeremy Harrison                                            1,866                --              *            1,866
Joan Harrison                                                933                --              *              933
Kerry N. Hite                                                947                --              *              947
Joel Hough                                                   947                --              *              947
Todd M. Hough                                                947                --              *              947
Lawrence A. and Kathleen M. Hough (6)                     16,891                --              *           16,891
JB Partners                                                5,244                --              *            5,244
Alan R. Katritzky                                          1,072                --              *            1,072
Klitsner Family & Co. No. A                                4,035                --              *            4,035
Charlene Ledbetter                                           690                --              *              690
Davis U. Merwin                                            2,017                --              *            2,017
Joseph E. Padulo                                             632                --              *              632
Louis Padulo                                               2,781                --              *            2,781
Robert B. Padulo                                             632                --              *              632
George W. Parshall                                           464                --              *              464
Jon B. Platt                                               7,986                --              *            7,986
Rex James Bates Revocable Trust                            2,017                --              *            2,017
John Semack                                                2,023                --              *            2,023
Al Simmons                                                   107                --              *              107
Sondra Somer                                                 107                --              *              107
Nancy Somer                                                   85                --              *               85
Jon and Cathy Somer                                          214                --              *              214
Pike H. Sullivan                                           2,017                --              *            2,017
Richard and Caroline Swett                                 2,017                --              *            2,017
Ivar Ugi                                                     214                --              *              214
Bert van Deun                                              8,070                --              *            8,070
Vertical Fund Associates LP                                6,122                --              *            6,122
Peter Wipf                                                 1,072                --              *            1,072
Chi-Huey Wong                                              1,340                --              *            1,340
Robert Zambias                                             2,144                --              *            2,144
Apple Tree Partners I, L.P. (2)                          710,400                --           1.4%          710,400
Freya Fanning & Co.                                       27,366                --              *           27,366
Oxford Bioscience Partners (Bermuda) II L.P.              92,053                --              *           92,053
Oxford Bioscience Partners (GS-Adjunct) II L.P.          106,865                --              *          106,865
Oxford Bioscience Partners II L.P.                       122,833                --              *          122,833
Jon B. Platt                                              13,683                --              *           13,683
Vertical Fund Associates LP                               13,683                --              *           13,683
</TABLE>

                                       15
<PAGE>   17
<TABLE>
<S>                                                     <C>                     <C>          <C>          <C>
Alexandria Real Estate Equities, L.P.                     75,187                --              *           75,187
Bank Julius Baer & Co. LTD                               320,636                --              *          320,636
BB BioVentures L.P. (7)                                  963,052                --           1.9%          963,052
MPM Asset Management Investors 1999 LLC (7)               11,536                --              *           11,536
MPM BioVentures Parallel Fund, L.P. (7)                  134,706                --              *          134,706

Other Selling Stockholders
--------------------------
Joan M. Jordan                                            60,000                --              *           60,000
Pamela L. Henthorne                                       60,000                --              *           60,000
William Michael Miller                                    60,000                --              *           60,000
Eldon Dwayne Morris                                       60,000                --              *           60,000
Norma Jean Odum                                           60,000                --              *           60,000
Quentine M. Roberts                                       60,000                --              *           60,000
Winifried A. Wobbe                                        60,000                --              *           60,000
John M. Sullivan                                         174,000                --              *          174,000
Michael B. Sullivan                                        7,500                --              *            7,500
Carol T. Sullivan                                          7,500                --              *            7,500
</TABLE>

-----------------

* Represents beneficial ownership of less than 1 percent.

(1)      The number of shares reflected in the table as being beneficially owned
         by each former Coelacanth stockholder includes shares, representing 10%
         of the shares reflected in the first column of this table as
         beneficially owned by such selling stockholder, that are held by an
         escrow agent and may be used to satisfy claims, if any, which we may
         have for breaches of representations, warranties or covenants made by
         Coelacanth in the merger agreement. The number of shares reflected in
         the first column of this table as beneficially owned by each former
         Coelacanth stockholder assumes that such stockholder validly tenders to
         us all certificates representing former shares of capital stock of
         Coelacanth and other required documents in accordance with the merger
         agreement.

(2)      Mr. Harrison was a director of Coelacanth before the merger. Mr.
         Harrison is managing partner of Apple Tree Partners.

(3)      Dr. Kolb was Vice President of Chemistry and Chief Operating Officer of
         Coelacanth before the merger, and presently serves as our Vice
         President of Chemistry.

(4)      Dr. Sharpless was a director of Coelacanth before the merger.

(5)      Mr. Boulton was Vice President of Technology Operations of Coelacanth
         before the merger, and presently serves as our Vice President of
         Technology Operations.

(6)      Mr. Hough was a director of Coelacanth before the merger.

(7)      Michael Steinmetz, Ph.D., a director of Coelacanth before the merger,
         is chairman of the board of MPM Asset Management, the general partner
         of BB BioVentures L.P., MPM Asset Management Investors 1999 LLC and MPM
         BioVentures Parallel Fund, L.P.


                              PLAN OF DISTRIBUTION

         The shares covered by this prospectus may be offered and sold from time
to time by the selling stockholders. The term "selling stockholder" includes
donees selling 500 or fewer shares received from a selling stockholder as a gift
after the effective date of the registration statement of which this prospectus
is a part. The selling stockholders will act independently of us in making
decisions with respect to the timing, manner and size of each sale. Such sales
may be made on one or more exchanges or in the over-the-counter market or
otherwise, at prices and under terms then prevailing or at prices related to the
then current market price or in negotiated transactions. The selling
stockholders have advised us that they may offer and sell the shares of common
stock offered by this prospectus in one or more of, or a combination of, the
following methods:

         -        purchases by a broker-dealer as principal and resale by such
                  broker-dealer for its own account pursuant to this prospectus;


                                       16
<PAGE>   18
         -        ordinary brokerage transactions and transactions in which the
                  broker solicits purchasers;

         -        block trades in which the broker-dealer so engaged will
                  attempt to sell the shares as agent but may position and
                  resell a portion of the block as principal to facilitate the
                  transaction;

         -        an over-the-counter distribution in accordance with the rules
                  of the Nasdaq National Market;

         -        through the Nasdaq National Market or any other securities
                  exchange or association that quotes the common stock;

         -        in privately negotiated transactions; and

         -        in options transactions.

         In addition, the selling stockholders have advised us that they may
sell shares of common stock in compliance with Rule 144, if available, or
pursuant to other available exemptions from the registration requirements under
the Securities Act, rather than pursuant to this prospectus.

         To the extent required, this prospectus may be amended or supplemented
from time to time to describe a specific plan of distribution. In connection
with distributions of the shares or otherwise, the selling stockholders have
advised us that they may enter into hedging transactions with broker-dealers or
other financial institutions. In connection with such transactions,
broker-dealers or other financial institutions may engage in short sales of the
common stock in the course of hedging the positions they assume with a selling
stockholder. The selling stockholders have advised us that they may also sell
the common stock short and redeliver the shares to close out such short
positions. The selling stockholders have advised us that they may also enter
into option or other transactions with broker-dealers or other financial
institutions which require the delivery to such broker-dealer or other financial
institution of shares offered by this prospectus, which shares such
broker-dealer or other financial institution may resell pursuant to this
prospectus (as supplemented or amended to reflect such transaction). The selling
stockholders have advised us that they may also pledge shares to a broker-dealer
or other financial institution, and, upon a default, such broker-dealer or other
financial institution may effect sales of the pledged shares pursuant to this
prospectus (as supplemented or amended to reflect such transaction).

         In effecting sales, broker-dealers or agents engaged by a selling
stockholder may arrange for other broker-dealers to participate. Broker-dealers
or agents may receive commissions, discounts or concessions from the selling
stockholder in amounts to be negotiated immediately prior to the sale.

         In offering the shares covered by this prospectus, a selling
stockholder and any broker-dealers who execute sales for such selling
stockholder may be deemed to be "underwriters" within the meaning of the
Securities Act in connection with such sales. Any profits realized by a selling
stockholder and the compensation of any broker-dealer may be deemed to be
underwriting discounts and commissions.

         In order to comply with the securities laws of certain states, if
applicable, the shares must be sold in such jurisdictions only through
registered or licensed brokers or dealers. In addition, in certain states the
shares may not be sold unless they have been registered or qualified for sale in
the applicable state or an exemption from the registration or qualification
requirement is available and is complied with.

         The selling stockholders have advised us that they may sell their
shares at market prices prevailing at the time of sale, at prices related to
such prevailing market prices, at negotiated prices or at fixed prices and that
the transactions listed above may include cross or block transactions.

         We have advised the selling stockholders that the anti-manipulation
rules of Regulation M under the Securities Exchange Act of 1934 may apply to
their sales of common stock and to the activities of the selling stockholders
and their affiliates. In addition, we will make copies of this prospectus
available to the selling stockholders for the purpose of satisfying the
prospectus delivery requirements of the Securities Act of 1933. The selling
stockholders have advised us that they may indemnify any broker-dealer that
participates in transactions involving the sale of the shares against certain
liabilities, including liabilities arising under the Securities Act.


                                       17
<PAGE>   19
         At the time a particular offer of shares is made, if required, a
prospectus supplement will be distributed that will set forth the number of
shares being offered and the terms of the offering, including the name of any
underwriter, dealer or agent, the purchase price paid by any underwriter, any
discount, commission and other item constituting compensation, any discount,
commission or concession allowed or reallowed or paid to any dealer, and the
proposed selling price to the public.

         We have agreed to indemnify the selling stockholders against certain
liabilities, including certain liabilities under the Securities Act.

         We have agreed with the selling stockholders that received shares of
our common stock in the Coelacanth merger to keep the registration statement of
which this prospectus constitutes a part effective until the earliest to occur
of:

         -        such time as all of the shares covered by this prospectus have
                  been disposed of pursuant to and in accordance with the
                  registration statement;

         -        the expiration of twenty-four months from the date the
                  registration statement is declared effective; or

         -        such time as all shares covered by this prospectus may be sold
                  by the selling stockholders in accordance with the
                  requirements of Rule 144 in a 90-day period.

         Each of the selling stockholders that received common stock in the
Coelacanth merger has entered into a stockholder agreement under which such
selling stockholder has agreed not to sell or otherwise transfer shares of
common stock received in the merger until: (i) the earlier of the effectiveness
of the registration statement of which this prospectus is a part or October 10,
2001 with respect to 50% of such shares; (ii) January 8, 2002 with respect to an
additional 20% of such shares; (iii) April 8, 2002 with respect an additional
20% of such shares; and (iv) July 12, 2002 for the final 10% of such shares. All
shares offered by this prospectus by a selling stockholder that received common
stock in the Coelacanth merger will be sold subject to the terms and conditions
of the stockholder agreement.

         All shares offered by this prospectus by any other stockholder will be
sold subject to the terms and conditions of the registration rights agreement
described in the section entitled "Selling Stockholders."

                                  LEGAL MATTERS

         The validity of the common stock offered by this prospectus has been
passed upon for us by Vinson & Elkins L.L.P., Houston, Texas.

                                     EXPERTS

         The financial statements, as of December 31, 1999 and 2000, and for
each of the three years in the period ended December 31, 2000, incorporated by
reference in this prospectus have been audited by Arthur Andersen LLP,
independent public accountants, as indicated in their report with respect
thereto, and are included herein in reliance upon the authority of said firm as
experts in giving said report.

                       WHERE YOU CAN FIND MORE INFORMATION

         We have filed with the SEC a registration statement on Form S-3 under
the Securities Act of 1933 regarding the offer and sale of shares of common
stock by the selling stockholders. This prospectus, which constitutes a part of
the registration statement, does not contain all of the information contained in
the registration statement, some items of which are contained in exhibits to the
registration statement as permitted by the rules and regulations of the SEC. For
further information about us and our common stock, please review the
registration statement and the exhibits filed as a part of it. Statements made
in this prospectus that describe documents may not necessarily be complete. We
recommend that you review the documents that we have filed with the registration


                                       18
<PAGE>   20
statement to obtain a more complete understanding of these documents. A copy of
the registration statement, including the exhibits filed as a part of it, may be
inspected without charge at the SEC's Public Reference Room, 450 Fifth Street,
N.W., Washington, D.C. 20549, and copies of all or any part of the registration
statement may be obtained from the SEC upon the payment of fees prescribed by
it. You may obtain information on the Public Reference Room by calling the SEC
at 1-800-SEC-0330. The SEC maintains a Web site at http://www.sec.gov that
contains reports, proxy and information statements and other information
regarding companies that file electronically with it.

         We are subject to the information and reporting requirements of the
Securities Exchange Act of 1934 and will file periodic reports, proxy statements
and other information with the SEC. You may inspect any of these documents as
described in the preceding paragraph. These reports, proxy statements and other
information may also be inspected at the offices of Nasdaq Operations, 1735 K
Street, N.W., Washington, D.C. 20006.

                       DOCUMENTS INCORPORATED BY REFERENCE

         The SEC allows us to "incorporate by reference" into this prospectus
information that we file with the SEC in other documents. This means that we can
disclose important information to you by referring to other documents that
contain that information. The information incorporated by reference is
considered to be part of this prospectus, except for information superseded by
information in this prospectus. We incorporate by reference the documents listed
below that we have previously filed with the SEC and any future filings we make
with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Securities Exchange
Act of 1934, prior to the termination of the offering of the securities covered
by this prospectus:

         -        our annual report on Form 10-K for the year ended December 31,
                  2000;

         -        our quarterly reports on Form 10-Q for the quarter ended March
                  31, 2001;

         -        our current report on Form 8-K dated June 13, 2001; and

         -        the description of our common stock contained in our
                  registration statement on Form 8-A filed with the Commission
                  on March 27, 2000 pursuant to Section 12 of the Securities
                  Exchange Act of 1934, including any amendments and reports
                  filed for the purpose of updating such description.

         Any statement contained in a document incorporated or deemed to be
incorporated by reference in this prospectus will be deemed to be modified or
superseded for purposes of this prospectus to the extent that a statement
contained in this prospectus or in any other subsequently filed document which
also is or is deemed to be incorporated by reference in this prospectus modifies
or supersedes that statement. Any statement that is modified or superseded will
not constitute a part of this prospectus, except as modified or superseded.

         Upon your written or oral request, we will provide you at no cost a
copy of any or all of the documents incorporated by reference in this
prospectus, other than the exhibits to those documents, unless the exhibits are
specifically incorporated by reference into this prospectus. You may request a
copy of these documents by contacting:

                  Investor Relations
                  Lexicon Genetics Incorporated
                  4000 Research Forest Drive
                  The Woodlands, Texas 77381
                  Telephone: (281) 364-0100



                                       19
<PAGE>   21
                                     PART II

                     INFORMATION NOT REQUIRED IN PROSPECTUS

ITEM 14.          OTHER EXPENSES OF ISSUANCE AND DISTRIBUTION.

         The estimated expenses payable by the Registrant in connection with the
issuance and distribution of the securities being registered (other than
underwriting discounts and commissions) are as follows:

<TABLE>
<S>                                                                      <C>
         SEC Registration Fee.................................           $      7,872
         Printing Expenses....................................                  5,000
         Accounting Fees and Expenses.........................                  5,000
         Legal Fees and Expenses..............................                  5,000
         Transfer Agent and Registrar Fees....................                    --
         Miscellaneous Expenses...............................                  2,128
                                                                         ------------
                   Total......................................           $     25,000
                                                                         ------------
</TABLE>


         The selling stockholders will pay any underwriting discounts and
commissions, brokerage fees and other expenses, including fees and expenses of
their counsel, if any, which discounts, commissions, fees and expenses are not
included in the foregoing table.

ITEM 15.          INDEMNIFICATION OF DIRECTORS AND OFFICERS.

         Section 145 of the Delaware General Corporation Law ("DGCL") provides
that a corporation may indemnify any person who was or is a party or is
threatened to be made a party to any threatened, pending or completed action,
suit or proceeding whether civil, criminal, administrative or investigative
(other than an action by or in the right of the corporation by reason of the
fact that he is or was a director, officer, employee or agent of the
corporation, or is or was serving at the request of the corporation as a
director, officer, employee or agent of another corporation, partnership, joint
venture, trust or other enterprise, against expenses (including attorneys'
fees), judgments, fines and amounts paid in settlement actually and reasonably
incurred by him in connection with such action, suit or proceeding if he acted
in good faith and in a manner he reasonably believed to be in or not opposed to
the best interests of the corporation, and, with respect to any criminal action
or proceeding, had no reasonable cause to believe his conduct was unlawful.
Section 145 further provides that a corporation similarly may indemnify any such
person serving in any such capacity who was or is a party or is threatened to be
made a party to any threatened, pending or completed action or suit by or in the
right of the corporation to procure a judgment in its favor by reason of the
fact that he is or was a director, officer, employee or agent of the corporation
or is or was serving at the request of the corporation as a director, officer,
employee or agent of another corporation, partnership, joint venture, trust or
other enterprise, against expenses (including attorneys' fees) actually and
reasonably incurred in connection with the defense or settlement of such action
or suit if he acted in good faith and in a manner he reasonably believed to be
in or not opposed to the best interests of the corporation and except that no
indemnification shall be made in respect of any claim, issue or matter as to
which such person shall have been adjudged to be liable to the corporation
unless and only to the extent that the Delaware Court of Chancery or such other
court in which such action or suit was brought shall determine upon application
that, despite the adjudication of liability but in view of all of the
circumstances of the case, such person is fairly and reasonably entitled to
indemnity for such expenses which the Delaware Court of Chancery or such other
court shall deem proper.

         Lexicon's certificate of incorporation and bylaws provide that
indemnification shall be to the fullest extent permitted by the DGCL for all
current or former directors or officers. As permitted by the DGCL, the
certificate of incorporation provides that directors of Lexicon shall have no
personal liability to Lexicon or its stockholders for monetary damages for
breach of fiduciary duty as a director, except (1) for any breach of the
director's duty of loyalty to Lexicon or its stockholders, (2) for acts or
omissions not in good faith or which involve intentional misconduct or knowing
violation of law, (3) under Section 174 of the DGCL or (4) for any transaction
from which a director derived an improper personal benefit.



                                      II-1
<PAGE>   22
ITEM 16.          EXHIBITS.

<TABLE>
<CAPTION>
EXHIBIT NO.        DESCRIPTION
-----------        -----------
<S>          <C>   <C>
3.1+         --    Restated Certificate of Incorporation (filed as Exhibit 3.1
                   to the Company's Registration Statement on Form S-1
                   (Registration No. 333-96469) and incorporated by reference
                   herein).

3.2+         --   Restated Bylaws (filed as Exhibit 3.2 to the Company's
                   Registration Statement on Form S-1 (Registration No.
                   333-96469) and incorporated by reference herein).

4.1*         --   Amended and Restated Registration Rights Agreement dated as
                   of May 7, 1998 by and among the Company and the stockholders
                   named therein.

4.2*         --   Form of Stockholder Agreement by and between the Company
                   and each former stockholder of Coelacanth Corporation.

5.1*         --   Opinion of Vinson & Elkins L.L.P.

23.1*        --   Consent of Arthur Andersen LLP

23.2*        --   Consent of Vinson & Elkins L.L.P. (contained in Exhibit
                   5.1)

24.1*        --   Power of Attorney (contained in signature page)
</TABLE>

----------------
+    Previously filed.
*    Filed herewith.


ITEM 17.          UNDERTAKINGS.

         The undersigned Registrant hereby undertakes:

                  (a) To file, during any period in which offers or sales are
         being made, a post-effective amendment to this Registration Statement:

                           (i) to include any prospectus required by Section
                  10(a)(3) of the Securities Act of 1933, as amended (the
                  "Securities Act");

                           (ii) to reflect in the prospectus any facts or events
                  arising after the effective date of this Registration
                  Statement (or the most recent post-effective amendment
                  thereof) which, individually or in the aggregate, represent a
                  fundamental change in the information set forth in this
                  Registration Statement. Notwithstanding the foregoing, any
                  increase or decrease in the volume of securities offered (if
                  the total dollar value of securities offered would not exceed
                  that which was registered) and any deviation from the low or
                  high end of the estimated maximum offering range may be
                  reflected in the form of prospectus filed with the Commission
                  pursuant to Rule 424(b) if, in the aggregate, the changes in
                  volume and price represent no more than 20 percent change in
                  the maximum aggregate offering price set forth in the
                  "Calculation of Registration Fee" table in the effective
                  Registration Statement; and

                           (iii) to include any material information with
                  respect to the plan of distribution not previously disclosed
                  in this Registration Statement or any material change to such
                  information in this Registration Statement;

         provided, however, that paragraphs (a)(i) and (a)(ii) do not apply if
         the information required to be included in a post-effective amendment
         by those paragraphs is contained in periodic reports filed by the
         Registrant pursuant to Section 13 or Section 15(d) of the Securities
         Exchange Act of 1934, as amended (the "Exchange Act"), that are
         incorporated by reference in this Registration Statement.

                  (b) That, for the purpose of determining any liability under
         the Securities Act, each such post-effective amendment shall be deemed
         to be a new registration statement relating to the securities offered
         therein, and the offering of such securities at that time shall be
         deemed to be the initial bona fide offering thereof.


                                      II-2
<PAGE>   23
                  (c) To remove from registration by means of a post-effective
         amendment any of the securities being registered which remain unsold at
         the termination of the offering.

         The Registrant hereby undertakes that, for purposes of determining any
liability under the Securities Act, each filing of the Registrant's annual
report pursuant to Section 13(a) or 15(d) of the Exchange Act (and, where
applicable, each filing of an employee benefit plan's annual report pursuant to
Section 15(d) of the Exchange Act) that is incorporated by reference in this
Registration Statement shall be deemed to be a new registration statement
relating to the securities offered therein and the offering of such securities
at the time shall be deemed to be the initial bona fide offering thereof.

         Insofar as indemnification for liabilities arising under the Securities
Act of 1933 may be permitted to directors, officers and controlling persons of
the Registrant pursuant to the provisions described in Item 14, or otherwise,
the Registrant has been advised that in the opinion of the Securities and
Exchange Commission such indemnification is against public policy as expressed
in the Act and is, therefore, unenforceable. In the event that a claim for
indemnification against such liabilities (other than the payment by the
Registrant of expenses incurred or paid by a director, officer or controlling
person of the Registrant in the successful defense of any action, suit or
proceeding) is asserted by such director, officer or controlling person in
connection with the securities being registered, the Registrant will, unless in
the opinion of its counsel the matter has been settled by controlling precedent,
submit to a court of appropriate jurisdiction the question whether such
indemnification by it is against public policy as expressed in the Act and will
be governed by the final adjudication of such issue.



                                      II-3
<PAGE>   24
                                   SIGNATURES

         Pursuant to the requirements of the Securities Act of 1933, the
Registrant certifies that it has reasonable grounds to believe that it meets all
of the requirements for filing on Form S-3 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of The Woodlands, in the State of Texas, on August 10,
2001.

                                  LEXICON GENETICS INCORPORATED

                                  By: /s/ Arthur T. Sands
                                     -------------------------------------------
                                           Arthur T. Sands, M.D., Ph.D.
                                           President and Chief Executive Officer

                                POWER OF ATTORNEY

         Each person whose signature appears below appoints Arthur T. Sands and
Jeffrey L. Wade, and each of them, any of whom may act without the joinder of
the other, as his true and lawful attorneys-in-fact and agents with full power
of substitution and resubstitution, for him and in his name, place and stead, in
any and all capacities, to sign any and all amendments (including post-effective
amendments) to this Registration Statement and any Registration Statement
(including any amendment thereto) for this offering that is to be effective upon
filing pursuant to Rule 462(b) under the Securities Act of 1933, as amended, and
to file the same, with all exhibits thereto, and all other documents in
connection therewith, with the Securities and Exchange Commission, granting unto
said attorneys-in-fact and agents full power and authority to do and perform
each and every act and thing requisite and necessary to be done, as fully to all
intents and purposes as he might or would do in person, hereby ratifying and
confirming all that said attorneys-in-fact and agents or any of them or their or
his substitute and substitutes, may lawfully do or cause to be done by virtue
hereof.

         PURSUANT TO THE REQUIREMENTS OF THE SECURITIES ACT OF 1933, AS AMENDED,
THIS REGISTRATION STATEMENT HAS BEEN SIGNED BELOW BY THE FOLLOWING PERSONS IN
THE CAPACITIES AND ON THE DATES INDICATED BELOW.


<TABLE>
<CAPTION>
                        Signature                                           Title                        Date
                        ---------                                           -----                        ----
<S>                                                            <C>                               <C>
                  /s/ Arthur T. Sands                          President, Chief Executive        August 10, 2001
-----------------------------------------------------          Officer and Director (principal
               Arthur T. Sands, M.D., Ph.D.                    executive officer)


                  /s/ Julia P. Gregory                         Executive Vice President, Chief   August 10, 2001
-----------------------------------------------------          Financial Officer (principal
                     Julia P. Gregory                          financial and accounting
                                                               officer)


              .   /s/ C. Thomas Caskey                         Chairman of the Board of          August 10, 2001
-----------------------------------------------------          Directors
                  C. Thomas Caskey, M.D.


                  /s/ Sam L. Barker                            Director                          August 10, 2001
-----------------------------------------------------
                   Sam L. Barker, Ph.D.


                  /s/ Gordon A. Cain                           Director                          August 10, 2001
-----------------------------------------------------
                      Gordon A. Cain

                  /s/ Patricia M. Cloherty                     Director                          August 10, 2001
-----------------------------------------------------
                   Patricia M. Cloherty
</TABLE>



                                      II-4
<PAGE>   25
<TABLE>
<S>                                                            <C>                               <C>
                  /s/ Robert J. Lefkowitz                      Director                          August 10, 2001
-----------------------------------------------------
                Robert J. Lefkowitz, M.D.


                  /s/ William A. McMinn                        Director                          August 10, 2001
-----------------------------------------------------
                    William A. McMinn
</TABLE>



                                      II-5
<PAGE>   26
                                  EXHIBIT INDEX

<TABLE>
<CAPTION>
EXHIBIT NO.             DESCRIPTION
-----------             -----------
<S>           <C>       <C>
3.1+           --       Restated Certificate of Incorporation (filed as Exhibit 3.1
                        to the Company's Registration Statement on Form S-1
                        (Registration No. 333-96469) and incorporated by reference
                        herein).

3.2+           --       Restated Bylaws (filed as Exhibit 3.2 to the Company's
                        Registration Statement on Form S-1 (Registration No.
                        333-96469) and incorporated by reference herein).

4.1*           --       Amended and Restated Registration Rights Agreement dated as
                        of May 7, 1998 by and among the Company and the stockholders
                        named therein.

4.2*           --       Form of Stockholder Agreement by and between the Company
                        and each former stockholder of Coelacanth Corporation.

5.1*           --       Opinion of Vinson & Elkins L.L.P.

23.1*          --       Consent of Arthur Andersen LLP

23.2*          --       Consent of Vinson & Elkins L.L.P. (contained in Exhibit
                        5.1)

24.1*          --       Power of Attorney (contained in signature page)
</TABLE>

-----------------------
+    Previously filed.
*    Filed herewith.

</TEXT>
</DOCUMENT>
<DOCUMENT>
<TYPE>EX-4.1
<SEQUENCE>3
<FILENAME>h89691ex4-1.txt
<DESCRIPTION>AMENDED REGISTRATION RIGHTS AGREEMENT
<TEXT>
<PAGE>   1
                                                                     Exhibit 4.1


                              AMENDED AND RESTATED
                          REGISTRATION RIGHTS AGREEMENT

      This Amended and Restated Registration Rights Agreement, dated as of May
7, 1998 (this "Agreement"), is entered into by and among Lexicon Genetics
Incorporated, a Delaware corporation (the "Company"), the persons listed on
Schedule A hereto (the "Common Holders") and the persons listed on Schedule B
hereto (the "Series A Holders").

                                   WITNESSETH:

      WHEREAS, the Company and the Common Holders are parties to a Registration
Rights Agreement dated as of September 14, 1995 (the "Existing Agreement")
pursuant to which the Common Holders possess certain rights with respect to the
registration of the offer and sale of shares of the Common Stock, par value
$0.001 per share ("Common Stock"), of the Company under the Securities Act of
1933, as amended; and

      WHEREAS, the Company proposes to enter into a Series A Preferred Stock
Purchase Agreement (the "Stock Purchase Agreement") with the Series A Holders
providing for the purchase by the Series A Holders of shares of the Series A
Preferred Stock, par value $0.01 per share ("Series A Preferred Stock"), of the
Company; and

      WHEREAS, the obligations of the Series A Holders under the Stock Purchase
Agreement are conditioned upon the execution and delivery of this Agreement by
the Company and the Common Holders;

      NOW, THEREFORE, the parties hereto agree as follows:

      1.    CERTAIN DEFINITIONS. As used in this Agreement, the following terms
shall have the meanings set forth below:

            (a)   "Cain Shares" shall mean the Common Shares issued by the
      Company to Gordon A. Cain.

            (b)   "Commercially Reasonable Best Efforts" when used with respect
      to an obligation to be performed or term or provision to be observed
      hereunder, shall mean such efforts (including, without limitation,
      expenditures of funds) as a prudent person seeking the benefits of such
      performance or action would make, use, apply or exercise to preserve,
      protect or advance its rights or interests.

            (c)   "Commission" shall mean the Securities and Exchange Commission
      or any other federal agency at the time administering the Securities Act.

            (d)   "Company" shall have the meaning set forth in the initial
      paragraph of this Agreement.

            (e)   "Common Holders" shall have the meaning set forth in the
      initial paragraph of this Agreement.

            (f)   "Common Stock" shall have the meaning set forth in the
      recitals of this Agreement.

            (g)   "Common Shares" shall mean the shares of Common Stock issued
      or issuable by the Company to the Common Holders and any shares of Common
      Stock issued as a dividend or other distribution with respect to or in
      exchange for or in replacement of such shares.


                                       1
<PAGE>   2
            (h)   "Conversion Shares" shall mean (i) the shares of Common Stock
      issued or issuable upon conversion of the Series A Preferred Stock, (ii)
      the shares of Common Stock issued or issuable upon the exercise of the
      warrants issued to Punk, Ziegel & Company in connection with the sale of
      the Series A Preferred Stock and (iii) any shares of Common Stock issued
      as a dividend or other distribution with respect to or in exchange for or
      in replacement of such shares.

            (i)   "Exchange Act" shall mean the Securities Exchange Act of 1934,
      as amended, or any similar successor federal statute and the rules and
      regulations thereunder, all as the same shall be in effect from time to
      time.

            (j)   "Holder" shall mean (i) any Common Holder who holds
      Registrable Securities, (ii) any Series A Holder who holds Registrable
      Securities and (iii) any other holder of Registrable Securities to whom
      the registration rights conferred by this Agreement have been transferred
      in compliance with Section 9 hereof.

            (k)   "Initiating Holders" shall mean (i) any Holder or Holders who
      in the aggregate hold at least 25% of the then-outstanding Cain Shares
      that constitute Registrable Securities or (ii) any Holder or Holders who
      in the aggregate hold at least 25% of the then-outstanding Conversion
      Shares that constitute Registrable Securities.

            (l)   "Person" means any individual, corporation, partnership, joint
      venture, association, joint-stock company, trust, unincorporated
      organization or government or other agency or political subdivision
      thereof.

            (m)   "Prospectus" means the prospectus included in any Registration
      Statement (including without limitation, a prospectus that discloses
      information previously omitted from a prospectus filed as part of an
      effective registration statement in reliance upon Rule 430A promulgated
      under the Securities Act), as amended or supplemented by any prospectus
      supplement, with respect to the terms of the offering of any portion of
      the securities covered by such Registration Statement, and all other
      amendments and supplements to the prospectus, including post-effective
      amendments, and all material incorporated by reference or deemed to be
      incorporated by reference in such prospectus.

            (n)   The terms "register," "registered" and "registration" shall
      refer to a registration effected by preparing and filing a Registration
      Statement in compliance with the Securities Act and applicable rules and
      regulations thereunder, and the declaration or ordering of the
      effectiveness of such Registration Statement.

            (o)   "Registrable Securities" shall mean (i) the Common Shares and
      (ii) the Conversion Shares, provided, however, that Registrable Securities
      shall not include any shares of Common Stock which have been disposed of
      pursuant to an effective Registration Statement, which have been sold or
      otherwise transferred under Rule 144 or which may be sold pursuant to Rule
      144(k) pursuant to the terms set forth herein.

            (p)   "Registration Expenses" shall mean all expenses incident to
      the Company's performance of or compliance with this Agreement including,
      without limitation: (i) all registration and filing fees, (ii) the fees
      and expenses of compliance with securities or blue sky laws (including
      fees and disbursements of


                                       2
<PAGE>   3
      counsel in connection with blue sky qualifications of the Registrable
      Securities), (iii) all printing, messenger and delivery expenses, (iv) the
      Company's internal expenses (including, without limitation, all salaries
      and expenses of its officers and employees performing legal or accounting
      duties), (v) the fees and expenses incurred in connection with the listing
      or quotation, as appropriate, of the Registrable Securities, (vi) the fees
      and disbursements of counsel for the Company and the fees and expenses for
      independent certified public accountants retained by the Company
      (including the expenses of any special audit or cold comfort letters),
      (vii) the fees and expenses of any special experts retained by the Company
      in connection with such registration, and (viii) the reasonable fees and
      expenses of one firm of counsel for the Series A Holders who are selling
      Registrable Securities pursuant to a Registration Statement, but shall not
      include Selling Expenses.

            (q)   "Registration Statement" means any registration statement of
      the Company which covers any of the Registrable Securities pursuant to the
      provisions of this Agreement, including the Prospectus, amendments and
      supplements to such Registration Statement, including post-effective
      amendments, all exhibits and all material incorporated by reference in
      such Registration Statement.

            (r)   "Rule 144" shall mean Rule 144 as promulgated by the
      Commission under the Securities Act, as such Rule may be amended from time
      to time, or any similar successor rule that may be promulgated by the
      Commission.

            (s)   "Rule 145" shall mean Rule 145 as promulgated by the
      Commission under the Securities Act, as such Rule may be amended from time
      to time, or any similar successor rule that may be promulgated by the
      Commission.

            (t)   "Securities Act" shall mean the Securities Act of 1933, as
      amended, or any similar successor federal statute and the rules and
      regulations thereunder, all as the same shall be in effect from time to
      time.

            (u)   "Selling Expenses" shall mean all underwriting discounts and
      selling commissions applicable to the sale of Registrable Securities and
      all fees and disbursements of counsel for any Holder (other than the fees
      and disbursements of counsel included in Registration Expenses or paid by
      the Company pursuant to Section 4).

            (v)   "Series A Holders" shall have the meaning set forth in the
      initial paragraph of this Agreement.

      2.    DEMAND REGISTRATION.

      2.1   Request for Registration. (a) If the Company shall receive from
Initiating Holders, at any time or times not earlier than 180 days after the
effective date of the first Registration Statement under the Securities Act
filed by the Company for an offering of its securities to the general public, a
written request (the "Request") that the Company effect any registration for the
offer and sale of all or a part of the Registrable Securities held by the
Holders participating in the proposed registration, for an amount of Shares
which is not less than 15% of the aggregate combined number of the then
outstanding shares held by Gordon A. Cain and the Series A Holders (calculated
as if all such outstanding shares have been converted into Common Stock), under
the Securities Act, the Company will:


                                       3
<PAGE>   4
            (i)   within ten (10) days of the receipt of the Request, give
      written notice of the proposed registration to all other Holders; and

            (ii)  as soon as practicable, use Commercially Reasonable Best
      Efforts to effect such registration (including, without limitation, filing
      a Registration Statement and any appropriate pre-effective or
      post-effective amendments, appropriate qualifications under applicable
      blue sky or other state securities laws, and appropriate compliance with
      the Securities Act) so as to permit or facilitate the sale and
      distribution of all or such portion of the Registrable Securities as are
      specified in such Request, together with all or such portion of the
      Registrable Securities of any Holder or Holders joining in such request as
      are specified in a written request received by the Company within 20 days
      after such written notice from the Company is effective.

      Each Request shall specify the amount of Registrable Securities proposed
to be sold and the intended method(s) of disposition thereof.

      (b)   The Company shall not be obligated to effect, or to take any action
to effect, any such registration pursuant to this Section 2:

            (i)   in any particular jurisdiction in which the Company would be
      required to execute a general consent to service of process in effecting
      such registration, qualification, or compliance, unless the Company is
      already subject to service in such jurisdiction and except as may be
      required by the Securities Act;

            (ii)  prior to the expiration of a period of twelve months after the
      Company has initiated any previous registration pursuant to this Section
      2.1, or after the Company has initiated a total of three such
      registrations pursuant to this Section 2.1; provided that the Company
      shall not be required to effect (A) more than two such registrations
      requested solely by Initiating Holders of Conversion Shares and (B) more
      than one such registration requested solely by Initiating Holders of Cain
      Shares; and provided further that a registration initiated pursuant to
      this Section 2.1 and subsequently withdrawn by the Holders registering
      shares therein shall not be counted as a requested registration pursuant
      to this clause (ii) if such withdrawal is based upon material adverse
      information relating to the Company that is not known by the Initiating
      Holders at the time of their request for registration pursuant to this
      Section 2.1 or if the Holders bear the Registration Expenses for such
      registration;

            (iii) during the period starting with the date 60 days prior to the
      Company's good faith estimate of the date of filing of, and ending on a
      date 180 days after the effective date of, a Company-initiated
      registration (other than a registration relating solely to employee
      benefit plans or a registration relating solely to a Rule 145
      transaction), provided that the Company is actively employing in good
      faith all Commercially Reasonable Best Efforts to cause such Registration
      Statement to become effective;

            (iv)  if the Initiating Holders do not request that such offering be
      firmly underwritten by underwriters selected by a majority in interest of
      the Initiating Holders (subject to the consent of the Company, which
      consent will not be unreasonably withheld); provided that the foregoing
      condition to the Company's obligation to effect a requested registration
      shall not apply in the event the registration may be effected on Form S-3;


                                       4
<PAGE>   5
            (v)   if the Company and the Initiating Holders are unable to obtain
      the commitment of the underwriters described in clause (iv) above, if
      applicable, to firmly underwrite the offer; or

            (vi)  if, within 14 days after its receipt of a written request to
      effect such registration, the Company causes to be delivered to the
      Initiating Holders an opinion of counsel reasonably acceptable to the
      Initiating Holders to the effect that the proposed disposition of
      Registrable Securities by the Holders wishing to dispose of their
      Registrable Securities pursuant to this Section 2 will not require
      registration or qualification under the Securities Act, it being
      specifically understood and agreed that such Holders will promptly furnish
      to the Company and such counsel all information such counsel may
      reasonably request in order to enable such counsel to determine whether it
      would be able to render such opinion.

      2.2   Right to Defer Registration. Subject to the provisions of Section
2.1(b), the Company shall use Commercially Reasonable Best Efforts to file a
Registration Statement covering the Registrable Securities so requested to be
registered as soon as practicable after receipt of the Request or Requests of
the Holders wishing to dispose of their Registrable Securities pursuant to this
Section 2; provided, however, that if (i) in the good faith judgment of the
Board of Directors of the Company, such registration would be seriously
detrimental to the Company and the Board of Directors of the Company concludes,
as a result, that it is essential to defer the filing of such Registration
Statement at such time, and (ii) the Company shall furnish to such Holders a
certificate signed by the President of the Company stating that in the good
faith judgment of the Board of Directors of the Company, it would be seriously
detrimental to the Company for such Registration Statement to be filed in the
near future and that it is, therefore, essential to defer the filing of such
Registration Statement, then the Company shall have the right to defer such
filing for the period during which such disclosure would be seriously
detrimental, provided that (except as provided in Section 2.1(b)(iii) above) the
Company may not defer the filing for a period of more than 90 days after receipt
of the request of the Initiating Holders, and, provided further, that the
Company shall not defer its obligation in this manner more than twice in any
twelve-month period.

      2.3   Underwriting. (a) If the registration requested by the Initiating
Holders is for a registered public offering involving an underwriting, the
Company shall so advise the Holders as a part of the written notice given
pursuant to Section 2.1 (a) above. In such event, the right of any Holder to
registration pursuant to Section 2 shall be conditioned upon such Holder's
participation in such underwriting and the inclusion of such Holder's
Registrable Securities in the underwriting to the extent provided herein. All
Holders proposing to distribute their securities through such underwriting
(together with the Company and other holders of securities of the Company
exercising registration rights with respect to such registration) shall enter
into an underwriting agreement in customary form with the representative of the
underwriter or underwriters selected by a majority in interest of the Initiating
Holders, subject to the consent of the Company, which consent shall not be
unreasonably withheld.

      (b)   Notwithstanding any other provision of this Section 2, if the
representative of the underwriters advises the Initiating Holders in writing
that marketing factors require a limitation on the number of shares to be
underwritten, the number of shares to be included in the underwriting or
registration shall be allocated first to the Holders of the same kinds of Shares
as the Initiating Holders (, Cain Shares or Conversion Shares) and thereafter as
set forth in Section 10 hereof. If a person who has requested inclusion in such
registration as provided above does not agree to the terms of any such
underwriting, such person shall be excluded therefrom by written notice from the
Company, the underwriter or the Initiating Holders. Any Registrable Securities
or other securities excluded or withdrawn from such underwriting shall also be
withdrawn from such registration. If shares are so withdrawn from the
registration and if the number of shares to be included in such registration was
previously reduced as a result of marketing factors pursuant to this Section
2.3, then the Company shall offer to all Holders who have retained rights


                                       5
<PAGE>   6
to include securities in the registration the right to include additional
securities in the registration in an aggregate amount equal to the number of
shares so withdrawn, with such shares to be allocated among such Holders
requesting additional inclusion first to the Initiating Holders with respect to
the Cain Shares and Conversion Shares requested to be included by the Initiating
Holders in such registration, then to the Holders of the same kinds of Shares as
the Initiating Holders (e.g., Cain Shares or Conversion Shares) and thereafter
in accordance with Section 10 hereof.

      3.    PIGGYBACK REGISTRATION.

      3.1   Notice of Registration. If the Company shall determine to register
any of its securities either for its own account or the account of a security
holder or holders exercising their respective demand registration rights (other
than pursuant to Section 2 hereof), other than a registration relating solely to
employee benefit plans, a registration relating solely to a Rule 145
transaction, or a registration on any registration form that does not permit
secondary sales, the Company will:

            (i)   promptly give to each Holder written notice thereof (but in no
      event less than 30 days before the anticipated date of filing); and

            (ii)  use Commercially Reasonable Best Efforts to include in such
      registration (and any related qualification under blue sky laws or other
      compliance), except as set forth in Section 3.2 below, and in any
      underwriting involved therein (to be included on the same terms and
      conditions as any similar securities of the Company or any other security
      holder included therein and to permit the sale or other disposition of
      such Registrable Securities in accordance with the terms of such
      underwriting), all the Registrable Securities specified in a written
      request or requests, made by any Holder within 20 days after the written
      notice from the Company described in clause (i) above is given. Such
      written request may specify all or a part of a Holder's Registrable
      Securities.

      3.2   Right to Terminate Registration. The Company shall have the right to
terminate or withdraw any registration initiated by it under this Section 3
prior to the effectiveness of such registration whether or not any Holder has
elected to include Registrable Securities in such registration. The Holders
shall be permitted to withdraw all or any part of the Registrable Securities
from a registration pursuant to this Section 3 at any time prior to the
effectiveness of such registration.

      3.3   Underwriting. (a) If the registration of which the Company gives
notice is for a registered public offering involving an underwriting, the
Company shall so advise the Holders as a part of the written notice given
pursuant to Section 3.1 above. In such event, the right of any Holder to
registration pursuant to this Section 3 shall be conditioned upon such Holder's
participation in such underwriting and the inclusion of such Holder's
Registrable Securities in the underwriting to the extent provided herein. All
Holders proposing to distribute their securities through such underwriting
(together with the Company and such other holders of securities of the Company
exercising registration rights with respect to such registration) shall enter
into an underwriting agreement in customary form with the representative of the
underwriter or underwriters selected by the Company or the security holders
initiating such registration, as the case may be.

      (b)   Notwithstanding any other provision of this Section 3, if the
representative of the underwriters advises the Company in writing that marketing
factors require a limitation on the number of shares to be underwritten, the
representative may (subject to the limitations set forth below) exclude all
Registrable Securities from, or limit the number of Registrable Securities to be
included in, the registration and underwriting. The Company shall so advise all
holders of securities requesting registration, and the amount of securities that
are


                                       6
<PAGE>   7
entitled to be included in the registration and underwriting shall be allocated
first to the Company for securities being sold for its own account and
thereafter as set forth in Section 10 hereof. If any person does not agree to
the terms of any such underwriting, such person shall be excluded therefrom by
written notice from the Company or the underwriter. Any Registrable Securities
or other securities excluded or withdrawn from such underwriting shall be
withdrawn from such registration.

      3.4   Continuing Obligation. No registration effected under this Section
3, and no failure to effect a registration under this Section 3, shall relieve
the Company of its obligation to effect a registration upon the request of
Holders pursuant to Section 2 (except as expressly provided therein), and no
failure to effect a registration under this Section 3 and to complete the sale
of Registrable Securities in connection therewith shall relieve the Company of
any other obligation under this Agreement (including, without limitation, the
Company's obligations to satisfy in full the Registration Expenses and its
obligations pursuant to Section 6.1).

      4.    EXPENSES OF REGISTRATION. All Registration Expenses incurred in
connection with any registration, qualification or compliance pursuant to this
Agreement, including the reasonable fees of one counsel for the selling
stockholders in the case of a registration pursuant to Section 2 or Section 3
shall be borne by the Company. All Selling Expenses relating to securities so
registered shall be borne by the holders of such securities pro rata on the
basis of the number of shares of securities so registered on their behalf.

      5.    REGISTRATION PROCEDURES. In the case of each registration effected
by the Company pursuant to this Agreement, the Company will keep each Holder
advised in writing as to the initiation of each registration and as to the
completion thereof. At its expense, the Company will use Commercially Reasonable
Best Efforts to:

            (a)   keep such registration effective for a period of 120 days or
      until the Holder or Holders have completed the distribution described in
      the Registration Statement relating thereto, whichever first occurs;
      provided, however, that such 120-day period shall be extended for a period
      of time equal to the period after the effectiveness of such requirements
      that the Holder refrains from selling any securities included in such
      registration at the request of an underwriter of Common Stock (or other
      securities) of the Company; provided further, however, that in the case of
      a Registration Statement on Form S-3 (or any substitute form that may be
      adopted by the Commission) the Company will keep such registration
      effective for a period of 5 years or until the Holders have completed the
      distribution of all of their Registrable Securities;

            (b)   promptly prepare and file with the Commission such amendments
      and post-effective amendments to the Registration Statement as may be
      necessary to keep such Registration Statement effective for as long as
      such registration is required to remain effective pursuant to the terms
      hereof; cause the Prospectus to be supplemented by any required Prospectus
      supplement, and, as so supplemented, to be filed pursuant to Rule 424
      under the Securities Act; and comply with the provisions of the Securities
      Act applicable to it with respect to the disposition of all Registrable
      Securities covered by such Registration Statement during the applicable
      period in accordance with the intended methods of disposition by the
      selling Holders set forth in such Registration Statement or supplement to
      the Prospectus;

            (c)   furnish such number of prospectuses and other documents
      incident thereto, including any amendment of or supplement to the
      prospectus, as a Holder from time to time may reasonably request;

            (d)   within a reasonable time period (to allow the opportunity, for
      review and comment, as set forth below) prior to filing a Registration
      Statement or a Prospectus or any amendment or supplement to


                                       7
<PAGE>   8
      such Registration Statement or Prospectus furnish to (i) each selling
      Holder, (ii) not more than one counsel, if any, representing all selling
      Holders, to be selected by a majority-in-interest of such selling Holders,
      and (iii) each underwriter, if any, of the Registrable Securities covered
      by such Registration Statement copies of such Registration Statement as
      proposed to be filed, together with exhibits thereto, for purposes of each
      such person's review and comment, and thereafter furnish to such selling
      Holders, counsel and underwriters, if any, for their review and comment
      such number of copies of such Registration Statement, each amendment and
      supplement thereto (in each case including all exhibits thereto and
      documents incorporated by reference therein), the Prospectus included in
      such Registration Statement (including each Prospectus subject to
      completion) and such other documents or information as such selling
      Holders, counsel or underwriters may reasonably request in order to
      facilitate the disposition of the Registrable Securities;

            (e)   notify each selling Holder of (and in any event within
      twenty-four (24) hours of the receipt of) any stop order issued or
      threatened by the Commission and take all reasonable actions required to
      prevent the entry of such stop order or to remove it at the earliest
      possible moment if entered;

            (f)   on or prior to the date on which the Registration Statement is
      declared effective by the Commission, use all reasonable efforts to (i)
      register or qualify the Registrable Securities under such other securities
      or blue sky laws of such jurisdictions in the United States as any selling
      Holder reasonably (in light of the intended plan of distribution)
      requests, and (ii) file documents required to register such Registrable
      Securities with or approved by such other governmental agencies or
      authorities in the United States as may be necessary by virtue of the
      business and operations of the Company and do any and all other acts and
      things that may be reasonably necessary or advisable to enable such
      selling Holder to consummate the disposition of the Registrable Securities
      owned by such selling Holder; provided that the Company will not be
      required to (A) qualify generally to do business in any jurisdiction where
      it would not otherwise be required to qualify but for this paragraph (f),
      (B) subject itself to taxation in any such jurisdiction or (C) consent to
      general service of process in any such jurisdiction;

            (g)   notify each selling Holder, selling Holders' counsel and any
      underwriter promptly (and in any event within 24 hours) and (if requested
      by any such Person) confirm such notice in writing, (i) when a Prospectus
      or any Prospectus supplement or post-effective amendment has been filed
      and, with respect to a Registration Statement or any post-effective
      amendment, when the same has become effective, (ii) of any request by the
      Commission or any other federal or state governmental authority for
      amendments or supplements to a Registration Statement or Prospectus or for
      additional information to be included in any Registration Statement or
      Prospectus or otherwise, (iii) of the issuance by the Commission of any
      stop order suspending the effectiveness of a Registration Statement or the
      initiation or threatening of any proceedings for that purpose, (iv) of the
      issuance by any state securities commission or other regulatory authority
      of any order suspending the qualification or exemption from qualification
      of any of the Registrable Securities under state securities or "blue sky"
      laws or the initiation of any proceedings for that purpose, and (v) of the
      happening of any event which makes any statement made in a Registration
      Statement or related Prospectus or any document incorporated or deemed to
      be incorporated by reference therein untrue or which requires the making
      of any changes in such Registration Statement, Prospectus or documents so
      that they will not contain any untrue statement of a material fact or omit
      to state any material fact required to be stated therein or necessary to
      make the statements in the Registration Statement and Prospectus not
      misleading in light of the circumstances under which they were made; and,
      as promptly as practicable thereafter, prepare and file with the
      Commission and furnish a supplement or amendment to


                                       8
<PAGE>   9
      such Prospectus so that, as thereafter deliverable to the purchasers of
      such Registrable Securities, such Prospectus will not contain any untrue
      statement of a material fact or omit to state a material fact necessary to
      make the statements therein, in light of the circumstances under which
      they were made, not misleading;

            (h)   make generally available an earnings statement satisfying the
      provisions of Section 11(a) of the Securities Act no later than ninety
      (90) days after the end of the 12month period beginning with the first day
      of the Company's first fiscal quarter commencing after the effective date
      of a Registration Statement, which earnings statement shall cover said
      12-month period, and which requirement will be deemed to be satisfied if
      the Company timely files complete and accurate information on Forms 10-Q,
      10-K and 8-K under the Exchange Act and otherwise complies with Rule 158
      under the Securities Act;

            (i)   if requested by the managing underwriter or underwriters,
      selling Holders' counsel, or any selling Holder, unless otherwise advised
      by counsel, promptly incorporate in a Prospectus supplement or
      post-effective amendment such information as the managing underwriter or
      underwriters request, or selling Holders' counsel requests, to be included
      therein, including, without limitation, with respect to the Registrable
      Securities being sold by such selling Holder to such underwriter or
      underwriters, the purchase price being paid therefor by such underwriter
      or underwriters and with respect to any other terms of the underwritten
      offering of the Registrable Securities to be sold in such offering, and
      promptly make all required filings of such Prospectus supplement or
      post-effective amendment;

            (j)   enter into customary agreements reasonably satisfactory to the
      Company (including, if applicable, an underwriting agreement in customary
      form and which is reasonably satisfactory to the Company) and take such
      other actions as are reasonably required in order to expedite or
      facilitate the disposition of such Registrable Securities (the selling
      Holders, at their option may, require that any or all of the
      representations, warranties and covenants of the Company to or for the
      benefit of such underwriters also be made to and for the benefit of such
      selling Holders);

            (k)   make available to each selling Holder (and will deliver to
      their counsel) and each underwriter, if any, subject to restrictions
      imposed by the United States federal government or any agency or
      instrumentality thereof, copies of all correspondence between the
      Commission and the Company, its counsel or auditors and will also make
      available for inspection at reasonable times at the Company's offices by
      any selling Holder of such Registrable Securities, any underwriter
      participating in any disposition pursuant to such Registration Statement
      and any attorney, accountant or other professional retained by any such
      Selling Holder or underwriter (collectively, the "Inspectors"), all
      financial and other records, pertinent corporate documents and properties
      of the Company as shall be reasonably necessary to enable them to exercise
      their due diligence responsibility, and cause the Company's officers and
      employees to supply all information reasonably requested by any Inspectors
      in connection with such Registration Statement;

            (1)   in connection with an underwritten offering, participate, to
      the extent reasonably requested by the managing underwriter or
      underwriters for the offering or the selling Holders, in customary efforts
      to sell the securities under the offering, including, without limitation,
      participating in "road shows"; provided that the Company shall not be
      obligated to participate in more than two such selling efforts in any
      12-month period;


                                       9
<PAGE>   10
            (m)   during the period when the Prospectus is required to be
      delivered under the Securities Act, promptly file all documents required
      to be filed with the Commission pursuant to Section 13(a), 13(c), 14 or
      15(d) of the Exchange Act;

            (n)   use all reasonable efforts to obtain a cold comfort letter
      from the Company's independent public accountants in customary form and
      covering such matters of the type customarily covered by cold comfort
      letters, as the selling Holders may request;

            (o)   cause all such Registrable Securities registered pursuant
      hereunder to be listed on each securities exchange on which similar
      securities issued by the Company are then listed;

            (p)   provide a transfer agent and registrar for all Registrable
      Securities registered pursuant to such Registration Statement and a CUSIP
      number for all such Registrable Securities, in each case not later than
      the effective date of such registration; and

            (q)   otherwise comply with all applicable rules and regulations
      of the Commission.

      6.    INDEMNIFICATION.

      6.1   Indemnification by the Company. The Company agrees to indemnify and
hold harmless, to the fullest extent permitted by law, each selling Holder, its
partners, officers, directors, employees and agents, and each Person, if any,
who controls such selling Holder within the meaning of Section 15 of the
Securities Act or Section 20 of the Exchange Act, together with the partners,
officers, directors, employees and agents of such controlling Person
(collectively, the "Controlling Persons"), from and against any loss, claim,
damage, liability, attorneys' fees, cost or expense and costs and expenses of
investigating and defending any such claim (collectively, the "Damages") and any
action in respect thereof to which such selling Holder, its partners, officers,
directors, employees and agents, and any such Controlling Person may become
subject under the Securities Act or otherwise, insofar as such Damages (or
proceedings in respect thereof) arise out of, or are based upon, any untrue
statement or alleged untrue statement of a material fact contained in any
Registration Statement or Prospectus or any preliminary Prospectus, or arise out
of, or are based upon, any omission or alleged omission to state therein a
material fact required to be stated therein or necessary to make the statements
therein not misleading under light of the circumstances in which they were made,
except insofar as the same are based upon information furnished in writing to
the Company by a Selling Holder expressly for use therein, and shall reimburse
each selling Holder, its partners, officers, directors, employees and agents,
and each such Controlling Person for any legal and other expenses incurred by
 .that selling Holder, its partners, officers, directors, employees and agents,
or any such Controlling Person in investigating or defending or preparing to
defend against any such Damages or proceedings; provided, however, that the
Company shall not be liable to any Holder or other indemnitee to the extent that
any such Damages arise out of or are based upon an untrue statement or omission
made in any preliminary prospectus if (i) such Holder failed to send or deliver
a copy of the final Prospectus with or prior to the delivery of written
confirmation of the sale by such Holder to the Person asserting the claim from
which such Damages arise, and (ii) the final Prospectus would have corrected
such untiiie statement or such omission; and provided further, however, that the
Company shall not be liable in any such case to the extent that any such Damages
arise out of or are based upon an untrue statement or omission in any Prospectus
if (x) such untrue statement or omission is corrected in an amendment or
supplement to such Prospectus, (y) having previously been furnished by or on
behalf of the Company with copies of such Prospectus as so amended or
supplemented, and (z) after being notified by the Company pursuant hereto of the
happening of any event which would make any statement in the Registration
Statement or related Prospectus or any document incorporated or deemed to be
incorporated by reference therein untrue or misleading, the Holder continues to
offer for sale the


                                       10
<PAGE>   11
Registrable Securities pursuant to the Registration Statement or Prospectus
which is the subject of such notice, such Holder thereafter fails to deliver
such Prospectus as so amended or supplemented prior to or concurrently with the
sale of a Registrable Security to the Person asserting the claim from which such
Damages arise; provided further, that the Company shall not be liable in any
case to the extent that any such Damages arise out of or are based upon an
untrue statement or omission in any Prospectus, even if an amended and corrected
Prospectus is not furnished to the Holder, but only to the extent that the
Holder, after being notified by the Company pursuant hereto, continues to use
such Prospectus and in such case and to the extent of, and with respect to,
Damages which arise after the Holder receives such notice. The Company also
agrees to indemnify any underwriters of the Registrable Securities, their
officers and directors and each Person who controls such underwriters on
substantially the same basis as that of the indemnification of the Selling
Holders provided in this Section 6.1.

      6.2   Indemnification by Selling Holders. Each selling Holder agrees,
severally but not jointly, to indemnify and hold harmless the Company, its
officers, directors, employees and agents and each Person, if any, who controls
the Company within the meaning of Section 15 of the Securities Act or Section 20
of the Exchange Act, together with the partners, officers, directors, employees
and agents of such controlling Person, to the same extent as the foregoing
indemnity from the Company to such selling Holder, but only with reference to
information related to such selling Holder, or its plan of distribution,
furnished in writing by such selling Holder expressly for use in any
Registration Statement or Prospectus, or any amendment or supplement thereto, or
any preliminary Prospectus. In case any action or proceeding shall be brought
against the Company or its officers, directors, employees or agents or any such
controlling Person or its officers, directors, employees or agents, in respect
of which indemnity may be sought against such selling Holder, such Selling
Holder shall have the rights and duties given to the Company, and the Company or
its officers, directors, employees or agents, or such controlling Person, or its
officers, directors, employees or agents, shall have the rights and duties given
to such selling Holder, by the preceding paragraph. Each selling Holder also
agrees to indemnify and hold harmless any underwriters of the Registrable
Securities, their officers and directors and each Person who controls such
underwriters on substantially the same basis as that of the indemnification of
the Company provided in this Section 6.2. Notwithstanding anything. contained
herein to the contrary, no selling Holder shall be required to indemnify such
underwriters or the Company or its officers, directors, employees or agents or
any such controlling Person or its officers, directors, employees or agents, for
any amount in excess of the net proceeds for the Registrable Securities sold for
the account of such selling Holder.

      6.3   Conduct of Indemnification Proceedings. Promptly after receipt by
any person in respect of which indemnity may be sought pursuant to Section 6.1
or 6.2 (an "Indemnified Party") of notice of any claim or the commencement of
any action, the Indemnified Party shall, if a claim in respect thereof is to be
made against the Person against whom such indemnity may be sought (an
"Indemnifying Party"), notify the Indemnifying Party in writing of the claim or
the commencement of such action; provided that the failure to notify the
Indemnifying Party shall not relieve it from any liability which it may have to
an Indemnified Party otherwise than under Section 6.1 or 6.2 except to the
extent of any actual prejudice resulting therefrom. If any such claim or action
shall be brought against an Indemnified Party, and it shall notify the
Indemnifying Party thereof, the Indemnifying Party shall be entitled to
participate therein, and, to the extent that it wishes, jointly with any other
similarly notified Indemnifying Party, to assume the defense thereof with
counsel reasonably satisfactory to the Indemnified Party. After notice from the
Indemnifying Party to the Indemnified Party of its election to assume the
defense of such claim or action, the Indemnifying Party shall not be liable to
the Indemnified Party for any legal or other expenses subsequently incurred by
the Indemnified Party in connection with the defense thereof other than
reasonable costs of investigation; provided that the Indemnified Party shall
have the right to employ separate counsel to represent the Indemnified Party and
its controlling Persons who may be subject to liability arising out of any claim
in respect of which


                                       11
<PAGE>   12
indemnity may be sought by the Indemnified Party against the Indemnifying Party,
but the fees and expenses of such counsel shall be for the account of such
Indemnified Party unless (i) the Indemnifying Party and the Indemnified Party
shall have mutually agreed to the retention of such counsel or (ii) in the
opinion of counsel to such Indemnified Party, representation of both parties by
the same counsel would be inappropriate due to actual or potential conflicts of
interest between them, it being understood, however, that the Indemnifying Party
shall not, in connection with any one such claim or action or separate but
substantially similar or related claims or actions in the same jurisdiction
arising out of the same general allegations or circumstances, be liable for the
fees and expenses of more than one separate firm of attorneys (together with
appropriate local counsel) at any time for all Indemnified Parties. No
Indemnifying Party shall, without the prior written consent of the Indemnified
Party, effect any settlement of any claim or pending or threatened proceeding in
respect of which the Indemnified Party is or could have been a party and
indemnity could have been sought hereunder by such Indemnified Party, unless
such settlement includes an unconditional release of such Indemnified Party from
all liability arising out of such claim or proceeding. Whether or not the
defense of any claim or action is assumed by the Indemnifying Party, such
Indemnifying Party will not be subject to any liability for any settlement made
without its consent, which consent will not be unreasonably withheld.

      6.4   Contribution. If the indemnification provided for in this Section 6
is unavailable to the Indemnified Parties in respect of any Damages referred to
herein, then each Indemnifying Party, in lieu of indemnifying such Indemnified
Party, shall contribute to the amount paid or payable by such Indemnified Party
as a result of such Damages in such proportion as is appropriate to reflect the
relative benefits but also the relative fault of the Company on the one hand and
the Selling Holders on the other in connection with the statements or omissions
which resulted in such Damages, as well as any other relevant equitable
considerations. The relative fault of the Company on the one hand and of each
selling Holder on the other shall be determined by reference to, among other
things, whether the untrue or alleged untrue statement of a material fact or the
omission or alleged omission to state a material fact relates to information
supplied by such party, and the parties' relative intent, knowledge, access to
information and opportunity to correct or prevent such statement or omission.

      The Company and the selling Holders agree that it would not be just and
equitable if contribution pursuant to this Section 6.4 were determined by pro
rata allocation or by any other method of allocation which does not take account
of the equitable considerations referred to in the immediately preceding
paragraph. The amount paid or payable by an Indemnified Party as a result of the
Damages referred to in the immediately preceding paragraph shall be deemed to
include, subject to the limitations set forth above, any legal or other expenses
reasonably incurred by such Indemnified Party in connection with investigating
or defending any such action or claim. Notwithstanding the provisions of this
Section 6.4, no selling Holder shall be required to contribute any amount in
excess of the amount by which the net proceeds for the Registrable Securities
sold for the account of the selling Holder exceeds the amount of any damages
which such selling Holder has otherwise paid by reason of such untrue or alleged
untrue statement or omission or alleged omission. No Person guilty of fraudulent
misrepresentation (within the meaning of Section 11 (f) of the Securities Act)
shall be entitled to contribution from any Person who was not guilty of such
fraudulent misrepresentation. Each selling Holder's obligations to contribute
pursuant to this Section 6.4 is several in the proportion that the proceeds of
the offering received by such selling Holder bears to the total proceeds of the
offering received by all the selling Holders and not joint.

      7.    INFORMATION AND OTHER OBLIGATIONS OF HOLDER.

      (a)   As a condition to exercising the registration rights provided for
herein, each Holder of Registrable Securities shall furnish to the Company such
information regarding such Holder and the distribution proposed by


                                       12
<PAGE>   13
such Holder as the Company may reasonably request in writing and as shall be
reasonably required in connection with any registration, qualification, or
compliance referred to in this Agreement.

      (b)   The failure of any Holder to furnish the information requested
pursuant to Section 7(a) shall not affect the obligation of the Company under
Sections 2 or 3 to the remaining Holder(s) who furnish such information unless,
in the reasonable opinion of counsel to the Company or the underwriters, if any,
such failure impairs or may impair the legality of the Registration Statement or
the underlying offering.

      (c)   Each Holder, with respect to any Registrable Securities included in
any registration, shall cooperate in good faith with the Company and the
underwriters, if any, in connection with such registration.

      (d)   Each Holder, with respect to any Registrable Securities included in
any registration, shall make no further sales or other dispositions, or offers
therefor, of such shares under such Registration Statement if, during the
effectiveness of such Registration Statement, an intervening event should occur
which, in the opinion of counsel to the Company, makes the Prospectus included
in such Registration Statement no longer comply with the Securities Act until
such time as such holder has received from the Company copies of a new, amended
or supplemented Prospectus complying with the Securities Act.

      8.    RULE 144 REPORTING. With a view to making available the benefits of
certain rules and regulations of the Commission that may permit the sale of the
Restricted Securities to the public without registration, the Company agrees to
use its best efforts to:

            (a)   make and keep public information regarding the Company
      available as those terms are understood and defined in Rule 144 under the
      Securities Act, at all times from and after 90 days following the
      effective date of the first Registration Statement under the Securities
      Act filed by the Company for an offering of its securities to the general
      public;

            (b)   file with the Commission in a timely manner all reports and
      other documents required of the Company under the Securities Act and the
      Exchange Act at any time after it has become subject to such reporting
      requirements; and

            (c)   so long as a Holder owns any restricted Registrable
      Securities, furnish to the Holder forthwith upon written request a written
      statement by the Company as to its compliance with the reporting
      requirements of Rule 144 (at any time from and after 90 days following the
      effective date of the first Registration Statement filed by the Company
      for an offering of its securities to the general public), and of the
      Securities Act and the Exchange Act (at any time after it has become
      subject to such reporting requirements), a copy of the most recent annual
      or quarterly report of the Company, and such other reports and documents
      so filed as a Holder may reasonably request in availing itself of any rule
      or regulation of the Commission allowing a Holder to sell any such
      securities without registration.

      9.    TRANSFER OR ASSIGNMENT OF REGISTRATION RIGHTS. The rights to cause
the Company to register securities granted to Holders by the Company under this
Agreement may be transferred or assigned by a Holder in connection with any
transfer or assignment of Registrable Securities; provided that any transfer or
assignment of the registration rights granted under this Agreement shall be
conditioned upon (i) the Company's being given written notice at the time of or
within a reasonable time after said transfer or assignment, stating the name and
address of the transferee or assignee and identifying the securities with
respect to which such registration rights are being


                                       13
<PAGE>   14
transferred or assigned and (ii) the assumption in writing by the transferee or
assignee of the obligations of a Holder under this Agreement.

      10.   ALLOCATION OF REGISTRATION OPPORTUNITIES. In any circumstance in
which all of the Registrable Securities requested to be included in a
registration on behalf of the Holders cannot be so included as a result of
limitations of the aggregate number of shares of Registrable Securities that may
be so included, the number of shares of Registrable Securities that may be so
included shall be allocated among the Holders requesting inclusion of shares pro
rata on the basis of the number of shares of Registrable Securities held by such
Holders. The Company shall not limit the number of Registrable Securities to be
included in a registration pursuant to this Agreement in order to include shares
held by stockholders with no registration rights or, with respect to
registrations under Section 2 hereof, in order to include in such registration
securities registered for the Company's own account or securities other than
Registrable Securities.

      11.   TERMINATION OF REGISTRATION RIGHTS. The right of any Holder to
request registration or inclusion of Registrable Securities held by such Holder
in any registration pursuant to Section 2 or 3 hereof shall terminate on the
earlier to occur of (i) such date as all Registrable Securities held by such
Holder (including any Registrable Securities that such Holder is entitled to
acquire upon conversion of Series A Preferred Stock or exercise of warrants)
have been sold under Rule 144 or an effective Registration Statement under the
Securities Act or may immediately be sold under Rule 144(k), or (ii) the fifth
anniversary of the completion of an initial public offering of Common Stock
pursuant to an effective Registration Statement under the Securities Act.

      12.   LIMITATIONS ON SUBSEQUENT REGISTRATION RIGHTS. The Company agrees
and covenants that it will not grant or allow any persons any registration
rights with respect to any securities of the Company which rights are superior
to the rights granted herein or which would reduce the number of Conversion
Shares or Cain Shares that would be included for the account of Initiating
Holders in any registration pursuant to Section 2 hereof, unless it shall first
have obtained the written consent of (i) the Holders of at least 75% of the
outstanding Registrable Securities, (ii) the Holders of at least 50% of the
outstanding Conversion Shares that constitute Registrable Securities, and (iii)
the Holders of at least 66-2/3% of the outstanding Cain Shares that constitute
Registrable Securities.

      13.   MISCELLANEOUS.

      13.1  Governing Law. This Agreement shall be governed in all respects by
the internal laws of the State of Delaware, without reference to the conflicts
of law principles thereof.

      13.2  Successors and Assigns. Except as otherwise provided herein, this
Agreement shall inure to the benefit of, and be binding upon, the successors,
assigns, heirs, executors and administrators of the parties hereto.

      13.3  Entire Agreement. This Agreement constitutes the full and entire
understanding and agreement between the parties with regard to the subjects
hereof. Without limiting the foregoing, this Agreement amends and restates the
Existing Agreement in its entirety.

      13.4  Notices, etc. All notices and other communications required or
permitted hereunder shall be in writing and shall be mailed by registered or
certified mail, postage prepaid, or otherwise delivered by hand or by messenger,
including Federal Express or similar courier services, addressed (a) if to a
Holder, to such Holder's address as set forth in the stock records of the
Company, or (b) if to the Company, to 4000 Research Forest Drive, The Woodlands,
Texas 77381 Attn: President, or at such other address as the Company shall have
furnished to the


                                       14
<PAGE>   15
Holders. Each such notice or other communication shall for all purposes of this
Agreement be treated as effective or having been given when delivered if
delivered personally, or:- if sent by mail or courier, at the earlier of its
receipt or 72 hours after the same has been deposited in a regularly maintained
receptacle for the deposit of the United States mail, addressed and mailed as
aforesaid.

      13.5  Counterparts. This Agreement may be executed in any number of
counterparts, each of which may be executed by less than all of the Holders,
each of which shall be enforceable against the parties actually executing such
counterparts, and all of which together shall constitute one instrument.

      13.6  Severability. Whenever possible, each provision of this Agreement
will be interpreted in such manner as to be effective and valid under applicable
law, but if any provision of this Agreement is held to be invalid, illegal or
unenforceable in any respect under any applicable law or rule in any
jurisdiction, such invalidity, illegality or unenforceability will not affect
such provision in any other jurisdiction, and this Agreement will be reformed,
construed and enforced in such jurisdiction as if such invalid, illegal or
unenforceable provisions had never been contained herein.

      13.7  Titles and Subtitles. The titles and subtitles used in this
Agreement are used for convenience only and are not to be considered in
construing or interpreting this Agreement.

      13.8  Amendment and Waiver. Except as expressly provided herein, this
Agreement, or any provision hereof, may be amended, waived, discharged or
terminated upon the written consent of the Company and the Holders of at least
75% of the then outstanding Registrable Securities; provided, however, that (i)
if any of the rights of the Holders of the Conversion Shares are adversely
affected by such amendment or waiver, the written consent of the Holders of at
least 50% of the outstanding Conversion Shares that constitute Registrable
Securities shall also be required, and (ii) if any of the rights of the Holders
of the Cain Shares are adversely affected by such amendment or waiver, the
written consent of the Holders of at least 66-2/3% of the outstanding Cain
Shares that constitute Registrable Securities shall also be required.

      IN WITNESS WHEREOF, the parties have executed this Agreement as of the
date first set forth above.

                                    LEXICON GENETICS INCORPORATED

                                    By: /s/ Arthur T. Sands
                                        --------------------------------------
                                          Arthur T. Sands, M.D., Ph.D.
                                          President and Chief Executive Officer


                                       15

</TEXT>
</DOCUMENT>
<DOCUMENT>
<TYPE>EX-4.2
<SEQUENCE>4
<FILENAME>h89691ex4-2.txt
<DESCRIPTION>FORM OF STOCKHOLDER AGREEMENT
<TEXT>
<PAGE>   1
                                                                     EXHIBIT 4.2

                              STOCKHOLDER AGREEMENT

         This Stockholder Agreement is made and entered into as of this ____ day
of ______________, 2001 by and among the undersigned stockholder (the
"Stockholder") of Coelacanth Corporation, a Delaware corporation (the
"Company"), Lexicon Genetics Incorporated, a Delaware corporation (the "Parent")
and Angler Acquisition Corp., a Delaware corporation and wholly owned subsidiary
of the Parent (the "Merger Sub"). This Agreement is being delivered pursuant to
Sections 4.11 and 5.3(h) of the Agreement and Plan of Merger dated as of June
__, 2001 (the "Merger Agreement") by and among the Parent, the Merger Sub and
the Company. Capitalized terms not otherwise defined herein shall have the
meanings ascribed to them in the Merger Agreement.

         WHEREAS, the Merger Agreement provides that it is a condition to the
obligations of the Parent and the Merger Sub to consummate and effect the Merger
Agreement and the transactions contemplated thereby that stockholders of the
Company holding at least 90% of the Company's outstanding common stock, $.0001
par value per share (the "Common Stock"), on a fully diluted, as-converted
basis, shall have executed and delivered this Agreement;

         WHEREAS, the Parent and the Merger Sub would not consummate and effect
the transactions contemplated by the Merger Agreement if such condition were not
satisfied;

         WHEREAS, the Stockholder expects to derive a significant benefit from
the consummation of the transactions contemplated by the Merger Agreement; and

         WHEREAS, the Stockholder desires to execute and deliver this Agreement
as an inducement to the Parent and the Merger Sub to consummate and effect the
transactions contemplated by the Merger.

         NOW, THEREFORE, in consideration of the foregoing and other good and
valuable consideration, the Stockholder hereby represents and warrants to and
agrees with the Parent and the Merger Sub as follows:

         1. Stockholder's Title and Authority. The Stockholder hereby represents
and warrants to the Parent and the Merger Sub that (a) the Stockholder has duly
authorized, executed and delivered this Agreement and this Agreement constitutes
a valid and binding agreement and neither the execution and delivery of this
Agreement nor the consummation by the Stockholder of the transactions
contemplated hereby will constitute a violation of, a default under, or conflict
with any contract, commitment, agreement, understanding, arrangement or
restriction of any kind to which the Stockholder is a party or by which the
Stockholder is bound; (b) consummation by the Stockholder of the transactions
contemplated hereby will not violate, or require any consent, approval, or
notice under, any provision of law applicable to the Stockholder; (c) the shares
of capital stock of the Company and options and warrants to acquire capital
stock of the Company as set forth on the signature page hereto (the "Shares")
and the certificates or other instruments representing same are now and, at the
Closing, will be, held by the Stockholder or by a nominee or custodian for the
benefit of the Stockholder, free and clear of all liens, claims, security
interests, proxies, voting trusts or agreements or any other encumbrances
whatsoever ("Encumbrances") with respect to the ownership or voting of the
Shares or otherwise, other than Encumbrances created by or arising pursuant to
the Agreement and Irrevocable Proxy previously executed by the Stockholder, if
so executed by the Stockholder, and there are no outstanding options, warrants
or rights to purchase or acquire, or proxies, powers-of-attorney, voting
agreements, trust agreements or other agreements relating to, the Shares other
than such Agreement and Irrevocable Proxy; (d) such Shares constitute all of the
securities of the Company owned beneficially or of record by the Stockholder on
the date hereof and as will be so owned on the Closing Date; and (e) the
Stockholder has the present power and right to vote all of the Shares (other
than options and warrants) that are entitled to vote.

         2. Stockholders' Representative. The Stockholder hereby irrevocably
ratifies and agrees to the appointment of Michael Steinmetz, on behalf of MPM
Asset Management, as the representative (the "Representative") of the
stockholders of the Company (provided that the Representative may be replaced in
accordance with Section 8.4 of the Merger Agreement) for the purpose of
administering the Merger Agreement on behalf of the Stockholder, to the extent
set forth in the Merger Agreement and the Indemnity Escrow Agreement, including
without limitation, signing the Indemnity Escrow Agreement, performing the
functions and acts of the Representative thereunder, delivering appropriate
instructions and executing any documents or agreements


                                       1
<PAGE>   2
necessary or desirable for carrying out the functions of the Representative
thereunder and otherwise administering the indemnification and escrow
distribution provisions set forth in Article 8 of the Merger Agreement. The
Stockholder agrees that the Parent and the Surviving Corporation shall be
entitled to deal exclusively with the Representative and that the Representative
shall have the authority to bind the Stockholder with respect to all such
matters arising under the Merger Agreement and the Escrow Agreement.

         3. Registration Rights. The Stockholder has reviewed, and hereby
understands, acknowledges and agrees to, the provisions relating to registration
set forth in Section 4.11 of the Merger Agreement and further agrees to provide
timely to the Representative the information relating to the Stockholder
required by Section 4.11(c) of the Merger Agreement. The Stockholder has
reviewed, and hereby acknowledges and agrees to be bound by and in accordance
with, the indemnification provisions and procedures set forth in Sections
4.11(g) and (h), respectively, of the Merger Agreement.

         4. Investment Intent. The Stockholder hereby represents and warrants to
each of the Parent and Merger Sub as follows: (i) the Stockholder is acquiring
the shares of Parent Common Stock to be issued pursuant to the Merger Agreement
and the Merger to such Stockholder solely for such Stockholder's account, for
investment purposes only and with no current intention or plan to distribute,
sell or otherwise dispose of any of those shares in connection with any
distribution in violation of the securities laws; (ii) the Stockholder is not a
party to any agreement or other arrangement for the disposition of any shares of
Parent Common Stock; (iii) the Stockholder is an "accredited investor" as
defined in Rule 501(a) under the Securities Act of 1933, as amended (the
"Securities Act"); (iv) the Stockholder (A) is able to bear the economic risk of
an investment in the Parent Common Stock acquired pursuant to the Merger
Agreement and the Merger, (B) can afford to sustain a total loss of that
investment, (C) has such knowledge and experience in financial and business
matters, and such past participation in investments, that he is capable of
evaluating the merits and risks of the proposed investment in the Parent Common
Stock, (D) has received and reviewed copies of the Merger Agreement, the Parent
SEC Reports and the Company's unaudited consolidated balance sheet dated April
30, 2001 and the Company's unaudited consolidated statement of operations for
the 10-month period ending on April 30, 2001; and (v) the Stockholder, if a
corporation, partnership, trust or other entity, acknowledges that it was not
formed for the specific purpose of acquiring the Parent Common Stock. Without
limiting any of the foregoing, the Stockholder acknowledges that the shares of
Parent Common Stock to be delivered to such Stockholder pursuant to the Merger
Agreement and the Merger have not been registered under the Securities Act or
qualified under applicable blue sky laws, and the Stockholder agrees not to
dispose of any portion of Parent Common Stock unless either (x) a registration
statement under the Securities Act is in effect as to the applicable shares and
the disposition is made in accordance with that registration statement, or (y)
an exemption from the registration requirements of the Securities Act is
available with respect to the applicable shares and the disposition is made in
accordance with that exemption; and, in the case of either (x) or (y), the
disposition is made in accordance with the provisions of Sections 6 and 7 of
this Agreement.

         5. Receipt and Release. As of the Closing and upon distribution of the
Purchase Price in accordance with the Merger Agreement, the Stockholder
acknowledges, confirms and agrees that the shares of Parent Common Stock
allocated to such Stockholder, and issued to such Stockholder or to the
Representative on behalf of such Stockholder, at the Effective Time pursuant to
the Merger and the Merger Agreement constitute in full such Stockholder's
proportionate share of the Purchase Price determined in accordance with Section
1.6 of the Merger Agreement and to which such Stockholder is entitled pursuant
to the Merger Agreement. The Stockholder hereby remits, releases, acquits and
forever discharges the Company, the Surviving Corporation and the Parent of and
from any Claims (as defined below) relating to the sufficiency or amount of
consideration allocated to and received by such Stockholder (or by the
Representative on behalf of such Stockholder) at the Effective Time pursuant to
the Merger Agreement and the Merger.

         As of the Closing, the Stockholder does hereby for the Stockholder and
any of the Stockholder's heirs, executors, administrators and legal
representatives remise, release, acquit and forever discharge the Company (and,
as of the Effective Time, the Surviving Corporation) of and from any and all
claims, demands, liabilities, responsibilities, disputes, causes of action and
obligations (collectively "Claims") of every nature whatsoever, liquidated or
unliquidated, known or unknown, matured or unmatured, fixed or contingent, which
such Stockholder now has, owns or holds or has at any time previously had, owned
or held against the Company including, without limitation, any and all Claims
arising out of the negligence, gross negligence or willful acts of the Company
and its employees and agents, whether any such Claim exists as of the Closing or
relates to any matter that occurred on or


                                       2
<PAGE>   3
prior to the Closing; provided, however, that, except as set forth in the
preceding paragraph, any Claim that may arise in connection with the failure of
any of the parties hereto to perform any of their obligations hereunder or under
the Merger Agreement or under any other agreement relating to the transactions
contemplated hereby or by the Merger Agreement or from any breaches by any such
party of any of such party's representations or warranties herein or in any
other agreement relating to the transactions contemplated hereby or by the
Merger Agreement shall not be remised, released, acquitted or discharged
pursuant to this Agreement.

         The Stockholder hereby represents and warrants that the Stockholder has
not previously assigned or transferred, or purported to assign or transfer, to
any person all or any part of any such Claims. The Stockholder covenants and
agrees not to assign or transfer to any person all or any part of any such
Claims. The Stockholder represents and warrants that the Stockholder has read
and understands all of the provisions of this Section 5 and that the Stockholder
has been represented by legal counsel of his own choosing in connection with the
negotiation, execution and delivery of this Agreement.

         6. Certain Prohibited Transactions. The Stockholder hereby agrees that,
except with the prior written consent of Parent, the Stockholder will not sell,
offer to sell, solicit offers to buy, dispose of, loan, pledge or grant any
right with respect to any Parent Common Stock issued to the Stockholder pursuant
to the Merger Agreement and the Merger (collectively, a "Disposition"), or
engage in any hedging or other transaction which is designed to or could
reasonably be expected to lead to or result in a Disposition of any such Parent
Common Stock by such Stockholder or any other person or entity. Such prohibited
hedging or other transaction shall include, without limitation, effecting any
short sale or having in effect any short position (whether or not such sale or
position is against the box and regardless of when such position was entered
into) or making any purchase, sale or grant of any right (including, without
limitation, any put or call option) with respect to any such Parent Common Stock
or with respect to any security (other than a broad-based market basket or
index) that includes, relates to or derives any significant part of its value
from Parent Common Stock.

         7. Restrictions on Sale of Parent Company Stock. The restrictions
described in Section 6 above will lapse as follows: (i) on the earlier to occur
of (A) the effective date of the Registration Statement or (B) the 90th day
after the Closing Date, with respect to 50% of the Parent Common Stock received
by the Stockholder pursuant to the Merger Agreement and the Merger, (ii) on the
180th day after the Closing Date with respect to 20% of such Parent Company
Stock, (iii) on the 270th day after the Closing Date with respect to 20% of such
Parent Company Stock and (iv) on the first anniversary of the Closing Date with
respect to the remainder of such Parent Common Stock, which remainder shall be
the Parent Common Stock held in escrow pursuant to the Indemnity Escrow
Agreement.

         8. Escrow. The Stockholder hereby acknowledges that the Stockholder has
reviewed Section 9.1 of the Merger Agreement, and agrees that Parent is entitled
to deduct from the Escrow Fund amounts equal to the Excess Expenses. The
Stockholder has reviewed and understands the indemnification provisions in
Articles 7 and 8 of the Merger Agreement and hereby agrees that the Escrow Fund
shall be available to satisfy such matters for which the Escrow Fund is
available under the terms of the Merger Agreement, subject to the limitations
and procedures set forth in Articles 7 and 8 of the Merger Agreement. The
provisions of Articles 7 and 8 of the Merger Agreement shall apply mutatis
mutandis to any such misrepresentation or breach by the Stockholder.

         9. Notices. Any notice, demand, or communication required or permitted
to be given by any provision of this Agreement shall be deemed to have been
sufficiently given or served for all purposes if (a) personally delivered, (b)
mailed by registered or certified first-class mail, prepaid with return receipt
requested, (c) sent by a nationally recognized overnight courier service, to the
recipient at the address below indicated or (d) delivered by facsimile which is
confirmed in writing by sending a copy of such facsimile to the recipient
thereof pursuant to clause (a) or (c) above:

                           If to Parent/Merger Sub:

                           Lexicon Genetics Incorporated
                           4000 Research Forest Drive
                           The Woodlands, TX 77381
                           Attn:  Dr. Arthur T. Sands, President and CEO
                           Telefax:  281-863-8088


                                       3
<PAGE>   4
                           with a copy to:

                           Vinson & Elkins, L.L.P.
                           1001 Fannin, Suite 2300
                           Houston, Texas 77002
                           Attention:  David Oelman
                           Telefax:  (713) 615-5861

                           If to the Stockholder:

                           ________________________

                           ________________________

                           ________________________

                           with a copy to:

                           ________________________

                           ________________________

                           ________________________

                           with a copy to:

                           Mintz Levin Cohn Ferris Glovsky and Popeo PC
                           One Financial Center

                           Boston, MA 02111
                           Attn:  Jonathan Kravetz
                           Telefax: ________________


or to such other address as any party hereto may, from time to time, designate
in a written notice given in like manner.

         Except as otherwise provided herein, any notice under this Agreement
will be deemed to have been given (x) on the date such notice is personally
delivered or delivered by facsimile, (y) four days after the date of mailing if
sent by certified or registered mail or (z) the next succeeding business day
after the date such notice is delivered to the overnight courier service if sent
by overnight courier; provided that in each case notices received after 4:00
p.m. (local time of the recipient) shall be deemed to have been duly given on
the next business day.

         10. Counterparts. This Agreement may be executed in one or more
counterparts, all of which shall be considered one and the same agreement and
each of which shall be deemed an original.

         11. Governing Law. This Agreement shall be construed under and governed
by the laws of the State of Delaware applicable to contracts made and to be
performed entirely within such state without giving effect to the provisions
thereof relating to conflicts of law.

         12. Amendment. This Agreement may not be amended, modified or
supplemented except upon the execution and delivery of a written agreement
executed by the parties hereto.

         13. Binding Effect; Assignment. The terms and provisions of this
Agreement shall be binding upon, inure to the benefit of and be enforceable by
the successors and permitted assigns of the parties hereto. No party hereunder
shall have the right to assign its rights hereunder or any interest herein
without the prior consent of the other parties hereto. Nothing in this Agreement
is intended or shall be construed to confer upon any person other than the
parties hereto and their respective permitted assigns any right, remedy or claim
under or by reason of this Agreement or any part hereof.


                                       4
<PAGE>   5
         14. Headings. The headings contained in this Agreement are for
reference only and shall not affect in any way the meaning or interpretation of
this Agreement.


         15. Construction. This Agreement has been negotiated by the Stockholder
and the Parent and their respective legal counsel, and legal and equitable
principles that might require the construction of this Agreement against the
party drafting this Agreement shall not apply in any construction or
interpretation of this Agreement.

         16. Severability. Any provision of this Agreement which is invalid,
illegal or unenforceable in any jurisdiction shall, as to that jurisdiction, be
ineffective to the extent of such invalidity, illegality or unenforceability,
without affecting in any way the remaining provisions hereof in such
jurisdiction or rendering that or any other provision of this Agreement invalid,
illegal or unenforceable in any other jurisdiction.

         17. Further Assurances. The Stockholder will, upon request, execute and
deliver any additional documents and take such further actions as may reasonably
be necessary or desirable to carry out the provisions hereof.


                                       5
<PAGE>   6
         IN WITNESS WHEREOF, the parties hereto have executed this Stockholder
Agreement as of this _____ day of __________, 2001.

                       ______________________________________
                       Signature of Stockholder

                       ______________________________________
                       Name of Stockholder

                       Shares Owned:

                       ___________ shares of Common Stock
                       ___________ shares of Series A Preferred Stock
                       ___________ shares of Series B Preferred Stock
                       ___________ shares of Series C Preferred Stock
                       ___________ shares of Series D Preferred Stock

                       Options and Warrants Owned:

                       Options to purchase ______________ shares of Common Stock

                       Warrants to purchase _____________ shares of Common Stock

Agreed and Accepted:

LEXICON GENETICS INCORPORATED


By:  ____________________________________
Name:____________________________________
Title:___________________________________


ANGLER ACQUISITION CORP.


By:  ____________________________________
Name:____________________________________
Title:___________________________________



                                       6

</TEXT>
</DOCUMENT>
<DOCUMENT>
<TYPE>EX-5.1
<SEQUENCE>5
<FILENAME>h89691ex5-1.txt
<DESCRIPTION>OPINION OF VINSON & ELKINS L.L.P.
<TEXT>
<PAGE>   1
                                                                     EXHIBIT 5.1




                                 August 10, 2001



Lexicon Genetics Incorporated
4000 Research Forest Drive
The Woodlands, Texas 77381

Re:   Registration Statement on Form S-3 of Lexicon Genetics Incorporated

Ladies and Gentlemen:

      We have acted as counsel to Lexicon Genetics Incorporated (the "Company"),
a Delaware corporation, with respect to certain legal matters in connection with
the Company's Registration Statement on Form S-3 (the "Registration Statement")
relating to the registration by the Company under the Securities Act of 1933, as
amended (the "Securities Act"), of the offer and sale by certain stockholders of
the Company from time to time, pursuant to Rule 415 under the Securities Act, of
up to 3,527,991 shares (the "Shares") of the Company's common stock, par value
$0.001 per share.

      We have examined originals or copies, certified or otherwise identified to
our satisfaction, of the Restated Certificate of Incorporation and Restated
Bylaws of the Company, each as amended to the date hereof, and such other
certificates, documents and instruments as we considered appropriate for
purposes of the opinion hereafter expressed.

      Based on the foregoing, we are of the opinion that the Shares have been
duly authorized and validly issued and are fully paid and non-assessable.

      The foregoing opinion is limited in all respects to the laws of the State
of Delaware and the federal laws of the United States of America.

      We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the reference to our firm under the caption "Legal
Matters" in the prospectus forming a part of the Registration Statement. By
giving such consent, we do not admit that we are within the category of persons
whose consent is required under Section 7 of the Securities Act or the rules and
regulations of the Securities and Exchange Commission issued thereunder.


                                    Very truly yours,


                                    VINSON & ELKINS L.L.P.
                                    /s/ VINSON & ELKINS L.L.P.

</TEXT>
</DOCUMENT>
<DOCUMENT>
<TYPE>EX-23.1
<SEQUENCE>6
<FILENAME>h89691ex23-1.txt
<DESCRIPTION>CONSENT OF ARTHUR ANDERSEN LLP
<TEXT>
<PAGE>   1
                                                                    EXHIBIT 23.1

                    CONSENT OF INDEPENDENT PUBLIC ACCOUNTANTS


      As independent public accountants, we hereby consent to the incorporation
by reference in this registration statement of our report dated February 27,
2001 included in Lexicon Genetics Incorporated's Form 10-K for the year ended
December 31, 2000, and to all references to our Firm included in this
registration statement.


/s/ ARTHUR ANDERSEN LLP



Houston, Texas
August 8, 2001

</TEXT>
</DOCUMENT>
</SUBMISSION>
