(Biotech Winners & Losers item updated for closing stock prices.)

NEW YORK ( TheStreet) -- Lexicon Pharmaceuticals ( LXRX - Get Report) stock was one of the leading gainers among biotech shares Monday on a day when most names in the land of experimental medicaments were in the green.

The Nasdaq Biotechnology Index jumped 6.24 points to 930.20

Shares of Lexicon, a Houston-based outfit that's attempting to develop treatments for diabetes, irritable bowel syndrome and rheumatoid arthritis, among other diseases, gained 4% to $1.79 Monday after earlier going as high as $1.91. Volume exceeded 1.9 million shares; average daily turnover has been about 750,000 shares.

Lexicon is expected to release results of a Phase Two clinical study of its rheumatoid arthritis drug LX2931. The firm launched the 12-week study in August 2009. On Friday, the company's CEO, Arthur Sands, is scheduled to deliver a presentation at the Biotech Industry Conference in New York.

Elsewhere, Exelixis ( EXEL - Get Report) shares added 21 cents, or 4.6%, to $4.81, on brisker-than-average volume. Earlier in the session, the stock hit $4.99.

Last week, the company licensed a pair of drugs still under development to Bristol-Myers Squibb ( BMY) for an initial payment of $60 million. The two companies will collaborate on developing the drugs, which could be used to treat diabetes and inflammatory illnesses, Exelixis says.

If certain milestones are hit, Exelixis said the Bristol-Myers deal could eventually result in payments of more than $500 million. Both drug programs are in preclinical trials.

Bristol-Myers in June walked away from a deal with Exelixis under which the companies were to have worked on a cancer drug. The two companies have five other licensing agreements in place.

SIGA Pharmaceuticals' ( SIGA - Get Report) stock continued to ride higher Monday, gaining more than 7% to $14.21. Last week, SIGA announced a tentative agreement to supply $500 million worth of smallpox antiviral treatments to the Department of Health and Human Services.

To make the deal official, though, SIGA needs to address a protest filed by a rival bidder for the government contract, one of the conditions of which is that the winner be certified as a small business. The Small Business Administration will rule on the protest.

Among other biotech gainers, Luminex ( LMNX) shares rose 4% to $16.59, Isis Pharmaceuticals ( ISIS) added 3.7% to $9.46 and Celera Corp. ( CRA) ended the day up 3.7% to $6.10.

Earnings season is upon us, and Gilead Sciences ( GILD - Get Report) was set to report third-quarter numbers after the bell Monday, with investors cued on sales of the company's HIV drug in European markets, where governments have ordered price cuts.

Gilead shares ended Monday's regular session down 0.5% to $37.54.

Other leading biotech decliners during the session included Acorda Therapeutics ( ACOR), which lost 4.7% to $27.57, Auxilium Pharmaceuticals ( AUXL), which closed Monday down 3.75% to $25.69, and Biodel ( BIOD), which fell 5% to $4.

Meanwhile, Molecular Insight Pharmaceuticals ( MIPI) shares were declining Monday after rocketing by as much as 80% Friday. The troubled company -- on the verge of being delisted by Nasdaq -- said an early-stage clinical trial of a cancer diagnostic test showed positive results vs. a rival technology.

The stock finished Monday by sinking 15.8% to $1.07. Also on Friday, Molecular Insight received another waiver extension from its bondholders as it struggles to refinance its debt load.

-- Written by Scott Eden in New York

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