The stock gained $3.80, or 8.3 percent, to $49.47 in midday trading. The shares have traded between $45.41 and $58.38 over the last 52 weeks, and are off 14 percent since the start of the year.

The patent dispute stretches back to 2005, when Barr asked the Food and Drug Administration to approve a generic version of Berlex and Schering AG's Yasmin. The companies then sued Barr. Germany-based Bayer AG bought Schering in 2006, becoming Bayer Schering Pharma AG, and inherited the ongoing lawsuit.

The Yasmin patent loss is part of a wider movement by generic drug developers to chip away at lucrative patents before they expire. Yasmin had sales of about $570 million in 2007. Other large generic drug companies, including Teva Pharmaceutical Industries Ltd. and Mylan Inc. are embroiled in their own Paragraph IV, or patent challenges, with big pharma.

Bayer has not yet said whether it will appeal the U.S. District Court for the District of New Jersey's ruling, which holds that the patent is invalid because it is obvious. However, the company has said it continues to retain exclusive distribution rights in the U.S. until March 2009.

Barr did not include sales of generic Yasmin in its 2008 guidance and stands to benefit as it will likely launch a generic version of in 2008, several analysts said.

"Despite a likely appeal, we believe that upon final approval, Barr will risk a launch to bolster a 2008 earnings outlook that was lackluster without patent wins," said Citi Investment Research analyst Andrew Swanson, reaffirming a "Hold" rating and upgrading his price target to $57 from $55.

He said Barr would face only a low risk of losing an appeal, citing prior case law, and added the decision could even effect the patent for Bayer's birth-control pill Yaz, which is a low-dose version of Yasmin.

Cowen and Co. analyst Ken Cacciatore reaffirmed a "Neutral" for Barr and said generic Yasmin sales could add between $80 million and $100 million to revenue in 2008 and then between $110 million and $140 million in 2009

"Given the lack of likely meaningful additional competition due to the difficult nature in manufacturing oral contraceptives, we believe that generic Yasmin should remain fairly stable for the following years thereafter," he said, in a note to investors.

Meanwhile, Goldman Sachs analyst Randall Stanicky and Banc of America analyst Frank H. Pinkerton reaffirmed "Buy" ratings for Barr.