WASHINGTON — The Supreme Court upheld Kentucky's use of lethal injection executions Wednesday.

The justices, by a 7-2 vote, turned back a constitutional challenge to the procedures in place in Kentucky, which uses three drugs to sedate, paralyze and kill inmates.

"We ... agree that petitioners have not carried their burden of showing that the risk of pain from maladministration of a concededly humane lethal injection protocol, and the failure to adopt untried and untested alternatives, constitute cruel and unusual punishment," Chief Justice John Roberts said in an opinion that garnered only three votes. Four other justices, however, agreed with the outcome.

Justices Ruth Bader Ginsburg and David Souter dissented.

Executions have been on hold since September, when the court agreed to hear the Kentucky case. There was no immediate indication when they would resume.

The argument against the three-drug protocol is that if the initial anesthetic does not take hold, the other two drugs can cause excruciating pain. One of those drugs, a paralytic, would render the prisoner unable to express his discomfort.

The case before the court came from Kentucky, where two death row inmates did not ask to be spared execution or death by injection. Instead, they wanted the court to order a switch to a single drug, a barbiturate, that causes no pain and can be given in a large enough dose to cause death.

At the very least, they said, the state should be required to impose tighter controls on the three-drug process to ensure that the anesthetic is given properly.

Kentucky has had only one execution by lethal injection and it did not present any obvious problems, both sides in the case agreed.

But executions elsewhere, in Florida and Ohio, took much longer than usual, with strong indications that the prisoners suffered severe pain in the process. Workers had trouble inserting the IV lines that are used to deliver the drugs.