It has been shown that anesthetic requirements during liver transplantation are inversely proportional to the degree of hepatic dysfunction. We investigate alterations during the three phases of requirements for intraoperative isoflurane within the target of 40 to 55 Bispectral Index (BIS) values concerning patients with end-stage liver disease who are undergoing liver transplantation. After faculty ethics committee approval, we studied 50 patients of (age range, 18 to 65 years) who were undergoing liver transplantation. After induction, we used isoflurane with air/oxygen (FiO(2) = 0.5%) for anesthestic maintenance. The isoflurane concentration was set within the range of 40 to 55 BIS values. Remifentanil (0.15 mu g/kg/min) was infused for analgesia and cisatracurium was administered via continuous infusion. After anesthetic induction, we inserted arterial, pulmonary artery, and central venous catheters. The heart rate, mean arterial pressure (MAP), mean pulmonary arterial pressure (MPAP), body temperature, BIS values, end-tidal isoflurane concentration (ETiso) and end-tidal carbon dioxide concentration (ETCO(2)) were recorded at 30-minute intervals during the dissection and neohepatic phases, at 15-minute intervals during the anhepatic phase. In addition, we calculated the cardiac index during the three phases. There was no difference in heart rates among the operative phases. In contrast, there were significant changes in MAP, MPAP, BIS, ETCO(2) and body temperature values. However, all of these parameters were in physiological ranges and clinically acceptable. The ETiso values were lowest in the anhepatic phase compared to other phases, but the differences were not clinically important. The ETiso values in the dissection and neohepatic phases were compared with the anhepatic phase higher 5% and 8.6% respectively. During liver transplantation, ETiso requirement for the anhepatic phase was lower compared with the other two phases within the range of 40 to 55 BIS values.