The justices voted 9-0 to block two Texas lawsuits, one that faulted Aetna for refusing to pay for a painkiller and one that said Cigna rushed a hysterectomy patient home from the hospital. The court said those suits are barred under a U.S. law that limits the liability of employer-sponsored benefit plans.

The ruling, which insulates insurers from damage claims by the 72 million Americans covered by HMO networks, comes four years after the court barred a different legal theory invoked by patients. Patients-rights advocates now will have to turn to Congress, where legislation to authorize suits has stalled.

``A regulatory vacuum exists,'' Justice Ruth Bader Ginsburg wrote, in a concurring opinion. She said that, while she agreed with the ruling, ``I also join the rising judicial chorus urging that Congress and this court revisit what is an unjust and increasingly tangled'' legal system for health-care claims.

The decision may thrust the issue into the presidential campaign. Democratic Senator John Kerry voted for legislation in 2001 that would have given patients a broad right to take their health insurers to court.

Republican President George W. Bush opposed that measure, saying it would have driven up health-care costs, and supported a scaled-back version. The legislative effort stalled when talks broke down between Senate Democrats and the White House.

In a court filing, the Bush administration urged the Supreme Court to bar the Texas lawsuits.

Internal Bleeding

In one of the disputes before the court, Aetna was sued by Juan Davila, who said he suffered internal bleeding and permanent harm after the HMO insisted he try a less-expensive pain medicine than Vioxx, which his doctor had prescribed.

In the other case, Cigna sought to end a lawsuit by Ruby Calad, who said she was sent home from the hospital too soon after her hysterectomy and later had to go to the emergency room. Calad said a Cigna representative overruled her doctor's recommendation that she needed to spend more than two days in the hospital.

Aetna and Cigna argued that damage suits are barred by a 1974 federal law governing employee benefit programs, the Employee Retirement Income Security Act, or ERISA. The companies said that, under ERISA, patients can seek payment from insurers only for the benefits they were denied, not for any pain and suffering they endured as a result.

The patients said their suits were akin to traditional state- court malpractice complaints against doctors, which the high court previously said are permissible under ERISA.

`Eligibility Decisions'

Justice Clarence Thomas wrote the opinion for the court. He said the HMOs were making ``pure eligibility decisions'' and weren't acting as treating physicians.

``With this decision, the court has signaled that predictability and uniformity in employee-benefit design trumps the personal-injury lawyer agenda,'' said Mark Merritt, president of the Pharmaceutical Care Management Association, which represents companies that manage pharmacy benefits.

Calad and Davila's attorney, George Parker Young, said the decision ``provides the HMOs with another tool to be used against the millions of workers and their families covered by ERISA.''

HMOs aim to control costs by requiring patients to go to certain doctors and get a referral before receiving care from a specialist.

Aetna and Cigna are the third- and fourth-largest U.S. health insurers respectively, behind No. 1 UnitedHealth Group Inc. and No. 2 WellPoint Health Networks Inc. Aetna shares fell 78 cents to $84.84 at 11:37 a.m. in New York Stock Exchange trading. Cigna fell 91 cents to $68.24.

Texas Law

Both lawsuits invoked a Texas law that authorized lawsuits when HMOs failed to provide ``ordinary care.''

As governor of Texas, Bush signed the measure. His administration nonetheless sided with the insurers and urged the justices to reject the Texas law.

About 40 to 50 suits have been filed against the managed- care networks in Texas in the past seven years, according to a lawyer for the patients. One jury awarded $13 million, although that amount was reduced on appeal.

Texas is one of 10 states with HMO liability laws. In other states, patients have sued HMOs under judge-made ``common law.''

The cases are Aetna Health v. Davila, 02-1845, and Cigna HealthCare of Texas v. Calad, 03-83.