WASHINGTON - In a case that could redefine ownership of technological or scientific innovations, the U.S. Supreme Court considered arguments Wednesday over whether patents can be applied to concepts drawn from laws of nature.

Lawyers from the Mayo Clinic asked justices to reject the patent held by Prometheus Laboratories that covers a diagnostic drug test for gastrointestinal disorders. Mayo argued the patent prevents the clinic from marketing its own version of the test at the cost of patient care.

Prometheus sued Rochester-based Mayo in 2004 for developing a drug dosage test that, like its own, used a scale to determine what dosages of medicine would be effective. A judge rejected the suit, concluding that natural phenomena and mental processes cannot be patented. The decision was overturned by the U.S. Court of Appeals for the Federal Circuit, leading Mayo to the Supreme Court.

The case has been hailed as potentially precedent-setting by hospitals, medical researchers, pharmaceutical companies, software developers, inventors and intellectual property lawyers. Indeed, the breadth of the justices' questions suggested that the high court may take a broad look at how far companies and individuals can go to claim a medical or scientific concept.

"All you do is point out facts that exist in the world and say, 'If you use them, you have to pay us,'" Justice Elena Kagan told Richard Bress, who represented Prometheus.

In contrast, Justice Antonin Scalia asked Mayo lawyer Stephen Shapiro, "Doesn't any medical patent rely on natural processes?"

Many of the justices focused on the scope of Prometheus' patent.

"I have a great idea," Chief Justice John Roberts said. "You take wood. You put it on a grate. You light it. And you get heat. I can get a patent for that?"

In order for Justice Stephen Breyer to participate in the case, his wife had to sell her Nestlé stock Wednesday morning after the court was informed the day before that Prometheus had been purchased by the Nestlé conglomerate this past summer. Breyer said the case boiled down to a simple question: "What has to be added to a law of nature to make it patentable?"

The Mayo Clinic argued that Prometheus' application of its patents to dozens of autoimmune disorders was so broad that any physician or researcher who knew about its dosage scale could be sued merely for thinking about the results of a blood test.

"Specificity is the key," Shapiro told Justice Anthony Kennedy. Patents must "leave room for others" to treat patients or do research. "We have to protect the storehouse of knowledge doctors need."

The Obama administration has come down on Mayo's side in this argument. "You can't get a patent by tacking a mental step onto an utterly conventional process for administering drugs and testing their effects," Solicitor General Donald Verrilli told the justices.

Prometheus' Bress said if Mayo's reasoning had been applied to other cases, whole classes of innovative research would not qualify for patents. As examples, he pointed to a patented system that uses certain bio-markers to decide if cancer drugs are working. He also cited a patented method for predicting where along the San Andreas Fault earthquakes might occur.

Shapiro, however, claimed that Mayo's test would be more accurate than the one from Prometheus, but the patent is not allowing Mayo to compete in the marketplace.

"You can't wipe out a whole field so no one else can have a competing test," Shapiro said. "The result for the public is that these numbers would be frozen for 20 years and a very serious person couldn't get a second opinion from Mayo Clinic, which uses different numbers."

In an interview after the hearing, Bress called the justices "clearly interested" in the issues at stake. Shapiro declined an interview request.

"With the case just being argued," said Mayo spokeswoman Kathleen Anderson, "we're going to sit back and wait."

A decision is not expected for several months.

The Associated Press contributed to this report.

Jim Spencer • 202-408-2752