San Francisco

Holders of valuable patents breathed a sigh of relief last week, when the US Supreme Court reversed a lower-court decision that many feared would pave the way for more copycat inventions.

In 2000, a federal appeals court upset supporters of tight patent protection by limiting the 'doctrine of equivalents'. This principle broadly states that a patent on blue nails can be extended to cover red nails as well, as their function is essentially the same.

In a decision known as the Festo ruling, the federal court had decreed that if a patent's claim had been narrowed during review — say from yellow and red nails to red nails only — it could not be widened again later by claiming equivalence. The case involved Festo Corporation, a machine-tool-maker in New York state, which argued that its patent on a part for a robotic arm should cover a similar device made by a Japanese rival.

As most patents are the product of negotiation with the Patent and Trademark Office, patent holders were worried that Festo would open the floodgates to close imitations of patented inventions.

In one related case, for example, MedImmune of Gaithersburg, Maryland, is fighting with the British biotechnology company Celltech to claim rights to an antibody for treating respiratory infections. MedImmune's version differs by one amino acid in 1,320 from Celltech's patented one.

One of the several petitions MedImmune filed with the Supreme Court argues that the doctrine of equivalents has been too widely interpreted, and should be limited as the federal court suggested.

But more than a dozen universities and research organizations, including Stanford University and the Massachusetts Institute of Technology, filed briefs urging the Supreme Court to undo the court judgement, which it did on 28 May.