The Wisconsin-based laboratory supply company Promega Corporation is claiming victory in the latest round of its battle with the pharmaceutical giant Hoffman-La Roche over patent rights to the naturally occuring form of the widely used laboratory enzyme 'Taq DNA polymerase'.

The enzyme is central to the 'polymerase chain reaction' or 'PCR' technique, with which researchers can cheaply and easily replicate stretches of DNA to produce large amounts of particular genes, without resorting to cloning them in bacteria or other microorganisms.

Based on complaints lodged by Promega, a federal district court in California ruled on Wednesday 8 December 1999 that the claims to the patent were 'unenforceable', on the grounds that the patent holder had intentionally withheld material information and distorted important facts in obtaining the patent.

Hoffman-La Roche purchased the rights to Taq DNA polymerase from the California company Cetus in 1991, and subsequently filed suit against Promega for continuing to sell Taq without the appropriate license.

The Wisconsin company filed a counter-suit, alleging that the Taq extracted by Cetus scientists was identical to enzymes that had already been described in the scientific literature. They also claimed that the scientists had been aware of this at the time of making their patent application, in which they claimed that the enzyme they described was entirely novel.

Although it is restricted to naturally-occuring Taq, Promega claims that this week's judgement, based on evidence presented at a trial in February before Judge Vaughn Walker of the Northern District of California in San Francisco, "sets the stage for a finding of unenforceability for all related Taq and PCR patents".

Although Roche says that the financial impact of the verdict will be minimal, Promega claims that, "in addition to the financial impact of lost sales and royalties, Roche faces the prospect of monetary damages and other sanctions.".

"The decision is a significant victory, particularly for the research community," said William Linton, chairman and chief executive office of Promega, in a statement. "The court has reaffirmed the importance of honesty and integrity on the part of scientists and companies in the pursuit of patents.".

A spokesperson for Roche said on Wednesday that the company intends to appeal against the verdict, adding that the company remained convinced that the scientists concerned with the original discovery had conducted themselves with integrity and professionalism.