Three groups of patients received Althesin, minaxolone or di-isopropyl phenol to supplement 67% nitrous oxide in oxygen. A fourth group receiving halothane to supplement nitrous oxide in oxygen acted as a control. Hepatic function tests were measured before operation and on days 1, 3, 5 and 7 after major vascular reconstructive surgery. There were significant increases to a mean value above the upper limit of normal in aspartate amino-transferase activity by day 3 in all groups. Total lactic dehydrogenase activity increased in the patients receiving Althesin, minaxolone and halothane. No change was seen in the alkaline phosphatase in any of the study groups. Gamma glutamyl transpeptidase increased in all groups, but the mean value at day 7 was not greater than the upper limit of normal. The mean activity of ornithine carbamoyl transpeptidase showed no change in any group throughout the study period. Two of the patients receiving minaxolone suffered cholestatic jaundice during the first month. These results suggest that anaesthesia with Althesin or di-isopropyl phenol results in enzyme changes similar to those seen in a comparable group of patients receiving halothane to supplement nitrous oxide in oxygen anaesthesia.