We have studied the effects of isoflurane or propofol anaesthesia on hepatic glutathione-S-transferase (GST) concentrations in 20 patients during and after prolonged plastic and reconstructive surgery (approximately 10 h). Mean plasma concentrations of GST did not exceed the normal range in any sample from any patient. Although GST concentrations in the propofol group were smaller than those in the isoflurane group, these differences were not statistically significant. These data show that prolonged propofol or isoflurane anaesthesia has no statistically significant effect on plasma concentrations of GST during and after extended surgery.