The case filed on behalf of condemned killer Michael Taylor had effectively halted Missouri executions since early last year. A judge said he wanted to be sure that the three-drug injection method did not cause risk of pain and suffering.
A three-judge panel of the 8th U.S. Circuit Court of Appeals found "no evidence to indicate that any of the last six inmates executed suffered any unnecessary pain," according to its ruling.
The court's decision reversed a ruling by U.S. District Judge Fernando Gaitan Jr. ordering reforms to Missouri's lethal injection procedures. He wanted the state to involve a doctor specializing in anesthesia, but the state has been unable to find a doctor willing to participate.
Missouri is among nine states that have put executions on hold as it grapples with whether lethal injection is inhumane.
Attorney General Jay Nixon said the decision "reopens the necessary legal avenue for the state of Missouri to move forward on this issue."
Margaret Phillips of the Eastern Missouri Coalition Against the Death Penalty said many questions remain unanswered and it would be unwise for the state to renew executions.
"The uncertainty of all of this is a good indication that Missouri needs a moratorium on the death penalty," she said.
A message seeking comment was left with the governor's office.
Taylor, convicted of killing 15-year-old Ann Harrison in Kansas City in 1989, was hours away from being put to death in February 2006 when the execution was halted. His attorney, Ginger Anders, said she would appeal Monday's ruling but declined further comment.