The United States attorney’s office in Massachusetts

subpoenaed in connection with its sales of bile duct

stents, broadening an investigation.

Abbott Laboratories and Boston Scientific, which also produce the stents, have said previously that they have been contacted by investigators.

The devices, also called biliary stents, are plastic or metal tubes intended to treat obstructions to the liver. They had an American market of about $40 million in 2007 for approved uses, according to the Millennium Research Group, a Toronto market research firm.

In February, Boston Scientific said the Justice Department was investigating whether manufacturers had been promoting the devices for unapproved uses, among them the repair of weakened blood vessels.

Boston Scientific, based in Natick, Mass., and Abbott, of Abbott Park, Ill., also have said they are cooperating.

Biliary stents are approved to treat obstructions in tubes that carry bile, a digestive fluid, to the intestines, but reports to the F.D.A. indicate that they are often inserted to prop open blood vessels in the legs. The reports also stated that unapproved uses may be injuring patients.

Once a medical product is approved by regulators, doctors are free to use it to treat any ailment. But F.D.A. guidelines say drug companies and device makers may not promote their products for unapproved purposes or patient categories, like prescribing adult medicines for children.