The Oklahoma Supreme Court has ruled two death row inmates have no right to learn the source of the drugs to be used to kill them, clearing the way for their execution.
Clayton Lockett, 38, and Charles Warner could be executed on 29 April.
Lawyers for the two argued they needed assurance the executions would not be botched with impure or expired drugs.
Last month, a judge ruled a law guarding the secrecy of the drugs' source was unconstitutional.
But on Wednesday, the state's highest court reversed that ruling.
"The plaintiffs have no more right to the information they requested than if they were being executed in the electric chair," Justice Steven Taylor wrote.
"If they were being hanged, they would have no right to know whether it be cotton or nylon rope; or if they were being executed by firing squad, they would have no right to know whether it be by Winchester or Remington ammunition," he added.
Gasped and choked
The court rulings come as US states are having increasing trouble obtaining drugs used in executions, amid an embargo from European pharmaceutical firms.
Critics say the states that are experimenting with other drugs risk botching executions and causing unnecessary suffering.
In January, for example, an execution in Ohio took 25 minutes to complete, as the inmate reportedly gasped and made choking noises in the moments before he was pronounced dead.
The state used two untried drugs to kill convicted murderer and rapist Dennis McGuire after the maker of the previous execution drug refused to allow its use.
Oklahoma state law blocks officials from revealing - even during court proceedings - the identities of the companies supplying the drugs used to sedate the inmates, paralyse their respiratory systems, and stop their hearts.
The challenge to Oklahoma's law was brought by Lockett, who was sentenced to death for the 1999 shooting of a 19-year-old woman, and Warner, who was convicted for the 1997 murder and rape of an 11-month-old girl.
The state said on 1 April that the men would be executed using midazolam, pancuronium bromide and potassium chloride - a combination never before used in Oklahoma, according to the Associated Press.