The justices, in a busy day for business-related cases, agreed to consider whether federal approval of medical devices shields manufacturers from product liability lawsuits in state courts. Most federal appeals courts have ruled that the Food and Drug Administration's regulation of medical devices does pre-empt such lawsuits.

Some confusion on the issue remains, however, which may have prompted the justices to take the case. In 2004, the Bush administration argued against the suits - a switch from the position the Clinton administration took.

''When even the federal government can't make up its mind on the plain meaning of the statute, it shows the need for an authoritative voice,'' said Allison Zieve, a lawyer for the plaintiffs in the case.

Zieve represents a New York couple, Charles and Donna Riegel, who sued Medtronic Inc. when its Evergreen balloon catheter burst during Charles Riegel's angioplasty. The balloon catheter is used to open patients' clogged arteries.

The case is Riegel v. Medtronic, (06-179).

Separately, the justices turned down an appeal from consumers who alleged that two pharmaceutical companies conspired to monopolize the market for a drug used to treat breast cancer.

At issue in the case was whether an agreement not to market a generic drug violates federal antitrust law.

Lawyers for the consumers said that an arrangement between generic drug maker Barr Pharmaceuticals Inc. and AstraZeneca PLC resulted in the extension of a monopoly on AstraZeneca's drug tamoxifen. The agreement resulted in Barr distributing unbranded tamoxifen at a price 5 percent less than Zeneca's Nolvadex brand.

Generic drugs are usually priced 30 percent to 80 percent below brand-name products, the consumers' lawyers said.

The case is Betty Joblove v. Barr, 06-830.

The justices also refused to hear an appeal by Lorillard Tobacco Co., a subsidiary of Loews Corp., in a trademark infringement case that some business groups considered critical to the fight against counterfeit goods.

The company said in court papers that fakes cost the U.S. economy $200 billion to $250 billion a year.

The case involved the sale of counterfeit Newport cigarettes by a small retailer in Denver, Colo. Lorillard sought an injunction against the retailer, but was turned down by the federal courts. The company argued the federal appeals court had made it too difficult to take action against retailers that sell counterfeit goods.

The case is Lorillard Tobacco Co. v. Engida, (06-1440).

Finally, the justices put off deciding on the Enron scandal, taking no action in a securities fraud case with billions of dollars at stake for victimized investors.

The case asks whether Enron shareholders can pursue a lawsuit against Wall Street investment banks that did business with the Texas energy company.

The justices have already agreed to consider a similar suit accusing two equipment manufacturers, Motorola Inc. and a unit of Cisco Systems Inc., of colluding with cable TV provider Charter Communications Inc. to deceive investors.

At issue in both cases is whether shareholders can collect damages from investment banks, attorneys and other parties that have aided fraud by their corporate clients.

The case is University of California Regents v. Merrill Lynch, 06-1341.