<PAGE>
                                                                    EXHIBIT 99.1


                          LEXICON GENETICS REPORTS 2005
                         THIRD QUARTER FINANCIAL RESULTS

THE WOODLANDS, TEXAS, NOVEMBER 1, 2005 -- Lexicon Genetics Incorporated (Nasdaq:
LEXG), a biopharmaceutical company focused on discovering and developing
breakthrough treatments for human disease, today reported financial results for
the three and nine months ended September 30, 2005.

REVENUES: Lexicon's revenues for the three months ended September 30, 2005
increased seven percent to $14.0 million from $13.1 million for the
corresponding period in 2004. The increase was primarily attributable to
collaborative research revenue recognized under Lexicon's alliance with Organon
and its award from the Texas Enterprise Fund for the creation of a knockout
mouse embryonic stem cell library. The third quarter of 2004 contained a
performance milestone payment received by Lexicon under its therapeutic protein
and antibody target discovery alliance with Genentech, Inc. The increase in
revenue from Lexicon's new agreements was partially offset by a decline in
subscription and license fees related to Lexicon's termination in December 2004
of the remaining subscription to its LexVision(R) database. For the nine months
ended September 30, 2005, revenues increased 17 percent to $41.8 million from
$35.7 million for the corresponding period of 2004.

RESEARCH AND DEVELOPMENT EXPENSES: Research and development expenses for the
three months ended September 30, 2005 increased four percent to $23.3 million
from $22.5 million for the corresponding period in 2004. The increase was
primarily the result of external research costs associated with preclinical and
scale-up activities for Lexicon's lead drug development programs and increased
personnel required to support the expansion and advancement of Lexicon's drug
discovery programs. For the nine months ended September 30, 2005, research and
development expenses increased three percent to $69.8 million from $67.5 million
for the corresponding period in 2004.

GENERAL AND ADMINISTRATIVE EXPENSES: General and administrative expenses for the
three months ended September 30, 2005 increased two percent to $4.7 million from
$4.6 million for the corresponding period in 2004. For the nine months ended
September 30, 2005, general and administrative expenses decreased three percent
to $13.9 million from $14.3 million for the corresponding period in 2004.

NET LOSS: Net loss for the three months ended September 30, 2005 decreased to
$14.1 million, or $0.22 per share, from a net loss of $14.4 million, or $0.23
per share, in the corresponding period in 2004. Net loss for the nine months
ended September 30, 2005 decreased to $42.2 million, or $0.66 per share, from a
net loss of $46.6 million, or $0.74 per share, in the corresponding period in
2004.

CASH AND INVESTMENTS: As of September 30, 2005, Lexicon had $90.2 million in
cash and investments, compared to $72.8 million as of June 30, 2005 and $87.6
million as of December 31, 2004. Cash and investments at September 30, 2005 was
favorably impacted by the receipt in August 2005 of $35 million pursuant to
Lexicon's award from the Texas Enterprise Fund for the creation of a genome-wide
knockout mouse embryonic stem cell library. Cash and investments includes
restricted cash and investments of $0.4 million on September 30, 2005, June 30,
2005 and December 31, 2004.

"We continue to demonstrate healthy revenue growth from collaborative research
and solid expense control, enabling us to narrow our net loss for the seventh
consecutive quarter-over-quarter period," said Julia P. Gregory, Lexicon's
executive vice president, corporate development and chief financial officer.
"Our newest collaborations have also had a positive impact on our cash and
investments."

<PAGE>
THIRD QUARTER 2005 HIGHLIGHTS

AWARD FROM TEXAS ENTERPRISE FUND: In July 2005, Lexicon announced it was awarded
$35 million from the Texas Enterprise Fund for the creation of a knockout mouse
embryonic stem cell library containing 350,000 cell lines. Lexicon will create
this new library using its proprietary gene trapping technology for the Texas
Institute for Genomic Medicine, a newly formed non-profit institute. In
addition, Lexicon will equip the Institute with the bioinformatics software
required for the management and analysis of data relating to the library. The
$35 million award was paid to Lexicon in August 2005.

CONTRACT WITH NATIONAL INSTITUTES OF HEALTH: Lexicon entered into a three-year
contract to provide selected knockout mouse lines and related phenotypic data to
the United States National Institutes of Health (NIH). Under the contract, NIH
may select lines of knockout mice and related phenotypic data from among lines
that Lexicon has elected to make available. These materials are related to genes
that have already been knocked out and analyzed by Lexicon. Lexicon will receive
payment from NIH of approximately $4.9 million for NIH's initial order of
knockout mouse lines. Lexicon retains the sole right to provide these materials
to commercial entities. NIH is obtaining these materials from Lexicon as a first
step in its recently announced Knockout Mouse Project, which has a goal of
obtaining a knockout for every gene.

"During the third quarter, several of our drug discovery programs made progress,
with compounds demonstrating proof-of-concept in preclinical testing," said
Arthur T. Sands, M.D., Ph.D., president and chief executive officer. "We utilize
our technology asset base to help fund our key strategic priorities -- drug
discovery and the rapid development of our lead programs."

LEXICON CONFERENCE CALL:

Dr. Arthur T. Sands and Julia P. Gregory will host a conference call at 11:00
a.m. Eastern Time on Tuesday, November 1, 2005 to review Lexicon's recent
operating highlights and its financial results for the nine months ended
September 30, 2005 and discuss the company's fourth quarter financial guidance.

The dial-in number for the conference call is 800-289-0552 (within the United
States) or 913-981-5536 (international). The pass code for all callers is
3420717. Investors can access www.lexicon-genetics.com to listen to a live
webcast of the call. The webcast will be archived and available for review
through November 4, 2005.

ABOUT LEXICON GENETICS

Lexicon Genetics is a biopharmaceutical company focused on the discovery and
development of breakthrough treatments for human disease. Lexicon is
systematically discovering the physiological and behavioral functions of genes
to identify potential points of therapeutic intervention, or drug targets.
Lexicon makes these discoveries using its proprietary gene knockout technology
to model the physiological effects that could be expected from prospective drugs
directed against novel targets. The Company has advanced knockout-validated
targets into drug discovery programs in six therapeutic areas: diabetes and
obesity, cardiovascular disease, psychiatric and neurological disorders, cancer,
immune system disorders and ophthalmic disease. Lexicon is working both
independently and through strategic collaborations and alliances to accelerate
the development and commercialization of its discoveries. Additional information
about Lexicon is available through its corporate website,
www.lexicon-genetics.com.

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SAFE HARBOR STATEMENT

         This press release contains "forward-looking statements," including
statements about Lexicon's growth and future operating results, discovery and
development of products, strategic alliances and intellectual property, as well
as other matters that are not historical facts or information. These
forward-looking statements are based on management's current assumptions and
expectations and involve risks, uncertainties and other important factors,
specifically including those relating to Lexicon's ability to successfully
conduct preclinical development of its drug candidates and advance such
candidates into clinical development, achieve its operational objectives, obtain
patent protection for its discoveries and establish strategic alliances, as well
as those relating to manufacturing, the regulatory process, intellectual
property rights, and the therapeutic or commercial value of its drug candidates,
that may cause Lexicon's actual results to be materially different from any
future results expressed or implied by such forward-looking statements.
Information identifying such important factors is contained under "Factors
Affecting Forward-Looking Statements" and "Business -- Risk Factors" in
Lexicon's annual report on Form 10-K for the year ended December 31, 2004, as
filed with the Securities and Exchange Commission. Lexicon undertakes no
obligation to update or revise any such forward-looking statements, whether as a
result of new information, future events or otherwise.

                                      # # #

CONTACT FOR LEXICON GENETICS:
Bobbie Faulkner
Manager, Investor Relations
(281) 863-3503
bfaulkner@lexgen.com

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                          LEXICON GENETICS INCORPORATED

                             SELECTED FINANCIAL DATA

<Table>
<Caption>
                                                                   THREE MONTHS ENDED           NINE MONTHS ENDED
CONSOLIDATED STATEMENTS OF OPERATIONS DATA                           SEPTEMBER 30,                SEPTEMBER 30,
                                                                 ----------------------      ----------------------
(In thousands, except per share data)                              2005          2004          2005          2004
                                                                 --------      --------      --------      --------
                                                                      (UNAUDITED)                  (UNAUDITED)
<S>                                                              <C>           <C>           <C>           <C>
Revenues:
   Collaborative research ..................................     $ 13,520      $ 11,492      $ 36,174      $ 27,997
   Subscription and license fees ...........................          443         1,617         5,612         7,732
                                                                 --------      --------      --------      --------
     Total revenues ........................................       13,963        13,109        41,786        35,729
Operating expenses:
   Research and development ................................       23,344        22,485        69,771        67,466
   General and administrative ..............................        4,674         4,573        13,856        14,259
                                                                 --------      --------      --------      --------
     Total operating expenses ..............................       28,018        27,058        83,627        81,725
                                                                 --------      --------      --------      --------
Loss from operations .......................................      (14,055)      (13,949)      (41,841)      (45,996)
Interest income ............................................          767           405         1,764         1,198
Interest expense ...........................................         (833)         (833)       (2,465)       (1,829)
Other income, net ..........................................           --            --           313            (4)
                                                                 --------      --------      --------      --------
Net loss ...................................................     $(14,121)     $(14,377)     $(42,229)     $(46,631)
                                                                 ========      ========      ========      ========
Net loss per common share, basic and diluted ...............     $  (0.22)     $  (0.23)     $  (0.66)     $  (0.74)
                                                                 ========      ========      ========      ========
Shares used in computing net loss per common share .........       64,134        63,422        63,767        63,286
</Table>

<TABLE>
<CAPTION>
CONSOLIDATED BALANCE SHEET DATA                                                          AS OF SEPTEMBER 30,      AS OF DECEMBER 31,
(In thousands)                                                                                  2005                     2004
                                                                                         -------------------      ------------------
                                                                                            (UNAUDITED)
<S>                                                                                      <C>                      <C>
Cash and investments, including restricted cash and investments of $430................      $  90,241                $  87,558
Property and equipment, net............................................................         85,996                   84,573
Goodwill...............................................................................         25,798                   25,798
Intangible assets other than goodwill, net.............................................            940                    1,840
Total assets...........................................................................        208,967                  211,980
Deferred revenue.......................................................................         79,495                   37,592
Current and long-term debt.............................................................         37,120                   37,631
Accumulated deficit....................................................................       (303,344)                (261,115)
Total stockholders' equity ............................................................         79,854                  121,594
</Table>
