Although the question before the court was the procedural one of how a challenge to lethal injection can be raised by a death row inmate who has exhausted the normal course of appeals, the intense argument showed that it was not easy to separate procedure from substance, at least with phrases like "excruciating pain" hanging in the courtroom air.
The case was brought by lawyers for Clarence E. Hill, who was convicted in 1983 of killing a police officer while fleeing a bank he had robbed in Pensacola, Fla.
Like every other death-penalty state except Nebraska, Florida executes by lethal injection. More precisely, like most other states, Florida uses a combination of three chemicals, one to anesthetize the inmate, a second to paralyze the muscles and a third to stop the heart.
Mr. Hill's lawyers argue that the combination, as administered by the Florida Department of Corrections, places inmates at risk of "wanton and gratuitous pain," in violation of the Eighth Amendment prohibition against cruel and unusual punishment.
Such a complaint would normally be brought as a petition for a writ of habeas corpus, the main pathway for a state inmate to get to federal court with a constitutional challenge to a conviction or sentence. But a 10-year-old federal law limits inmates to a single federal habeas petition, a quota Mr. Hill met long ago.
Mr. Hill's lawyers are trying another route, a Reconstruction-era civil rights law, known as Section 1983, that permits suits for constitutional violations. The question for the Supreme Court is whether that route is open.
Challenges to lethal injection, described as more humane than electrocution or hanging when it gained favor in the 1980's, have erupted in recent months, after publication a year ago in the Lancet, a British medical journal, of a study of lethal injection in the United States.
The article concluded that because of improper administration of anesthesia by nonmedical prison employees, a substantial proportion of those executed by injection might have died while experiencing severe pain.
Federal judges have granted stays of execution to explore the matter.
A North Carolina inmate, William Brown Jr., was executed last week after a federal judge ordered prison authorities to obtain and use a monitoring device to make sure Mr. Brown was properly anesthetized.
In California, the execution of Michael A. Morales has been put off since February, and the federal appeals court in San Francisco will hear arguments next week on how to proceed after anesthesiologists in the state refused to participate in executions.
Addressing the justices on Wednesday, Mr. Hill's lawyer, D. Todd Doss, said his client "does not challenge the state's right to execute him by lethal injection." Rather, Mr. Doss said, it was the "particular procedure" Florida proposes to use that was the problem. He added that if Mr. Hill won his case, the state could still execute him by "more humane means."
"Means which you decline to specify," Justice Antonin Scalia interjected, adding that if the state did come up with an alternative, "you can object to that as well" and "another few years will go by."
For several reasons, the question of whether there was an acceptable lethal-injection protocol, and whether it was the obligation of Mr. Hill's legal team to identify and accept it at this stage in the proceedings, dominated much of the hourlong argument.
One reason was that two years ago, the court permitted an Alabama inmate, David L. Nelson, to use Section 1983 to challenge the state's proposed injection procedure. Mr. Nelson's veins had collapsed from years of drug use, making it medically impossible to administer the injection in the normal way.
Since then, Mr. Nelson has managed to avoid execution by raising new challenges.
"The tale of Nelson's machinations and manipulations is part tragedy, part farce," Kevin C. Newsom, Alabama's solicitor general, told the justices in a brief that Alabama, supported by 24 other states, filed with the Supreme Court on Florida's behalf in this case, Hill v. McDonough, No. 05-8794.
The justices' emphasis on alternatives was also based on the distinction between a lawsuit under Section 1983 and a habeas corpus petition, the heart of the case at this stage. A Section 1983 suit challenges conditions of confinement, while a habeas corpus case challenges the sentence itself.
Chief Justice John G. Roberts Jr. observed at one point: "If he's unwilling to say there is a valid method, then the challenge is to the execution itself, and it has to be habeas."
The justices also had many questions for Mr. Doss about why he waited until Jan. 20, four days before Mr. Hill's scheduled execution date, to bring the lawsuit.
Florida's arguments did not go unchallenged. Addressing Carolyn M. Snurkowski, Florida's assistant deputy attorney general, Justice David H. Souter said that "the Lancet article has been out for a while, yet we have not heard a word that Florida has made any effort whatsoever" to avoid the problem of "gratuitous pain" that the article identified.