We investigated the effects of low-dose prostaglandin E1 (PGE1) on intra- and post-operative liver function in 109 adult patients undergoing upper abdominal surgery. Patients were divided into 2 groups; Control group (n = 42) and PGE1 group (n = 67). In PGE1 group, PGE1 was infused throughout surgery at a rate of 0.02 microgram kg-1 min-1. In both groups, anesthesia was maintained with a combination of inhalational and thoracic epidural anesthesia. Epidural anesthesia was maintained with 1.5% lidocaine infused epidurally at a constant rate (8 +/- 2 ml.hr-1). The continuous epidural infusion of lidocaine was initiated before surgery and discontinued at the end of surgery. Preoperative and postoperative liver function was evaluated with blood chemistry examination. Intraoperative liver function was evaluated in 84 patients (33 in control group and 51 in PGE1 group) by measuring plasma lidocaine concentration. Plasma lidocaine concentration was determined 1 and 3 hours after the initiation of lidocaine infusion and 0 and 2 hours after its termination. There were no differences between the groups in doses and infusion rates of lidocaine. In both groups, lidocaine concentration increased progressively as infusion was continued. Lidocaine concentration was significantly lower in PGE1 group than in control group at the end of the infusion. In 22 patients in control group and 35 in PGE1 group who received high-dose lidocaine (> 8 mg.kg-1), lidocaine concentration remained significantly lower in PGE1 group than in control group throughout the infusion period. The difference in lidocaine concentrations between the groups increased progressively as infusion was continued, though the doses and the infusion rates of lidocaine were not different between the groups. Postoperative liver function did not differ between the groups. Because removal of lidocaine from blood to liver parallels hepatic blood flow, the lower plasma lidocaine concentration in PGE1 group indicated that hepatic blood flow was higher and liver function was better-maintained with PGE1 during anesthesia and surgery. Low dose PGE1 thus improved intraoperative liver function during upper abdominal surgery.