Intravenous glucose tolerance tests were performed on 12 surgical patients the day before surgery and during surgery. Six patients were anesthetized with enflurane and six were operated on during an epidural lumbar blockade (Th8-S5). In the general anaesthesia group the plasma glucose concentration was significantly higher after the intraoperative glucose load than after the preoperative load. The pre- and intraoperative glucose tolerance tests were identical in the epidural group. Pre- and intraoperative glucose disappearance rates and plasma insulin responses were similar in the two groups, indicating that the observed differences in plasma glucose were caused by differences in hepatic glucose release, rather than differences in peripheral glucose utilization.