The US state of Missouri plans to execute a man even though he has a brain tumour, with his lawyers saying the lethal injection will cause him great pain.
Ernest Johnson, 55, has lost all appeals and is scheduled to be put to death after 6pm on Tuesday (local time).
Johnson was convicted of beating three people to death at a petrol station in 1994.
He suffers from a slow growth brain tumour that was partially removed in 2008.
The execution will be carried out with drugs including pentobarbital, which numbs the central nervous system including parts of the brain.
Johnson's lawyers say the use of this drug will cause him to experience convulsions and excruciating pain.
The 8th Amendment of the US Constitution bars "cruel and unusual punishment".
Johnson's lawyers now also say executing him in the gas chamber would reduce chances that he would suffer great pain.
In a ruling last week, a court in Missouri admitted that Johnson might suffer a death so painful as to violate the constitution.
But it said Johnson did not propose any alternative that would allow his execution to proceed swiftly. So the judge rejected his appeal.
"Missouri does not have a working gas chamber," Missouri Department of Corrections spokesman David Owen said on Monday.
Johnson's lawyer did not respond to requests for comment.
The execution comes amid heated debate in the US over the use of lethal injections to put people to death, particularly after botched executions in which inmates appeared to suffer.