Changes in arterial ketone body ratio(AKBR) during and after liver surgery were investigated in 11 patients who underwent partial hepatectomy or orthotopic liver transplantation during the period from April 1995 through June 1995. During partial hepatectomy, hepatic vascular occlusion induced reduction in AKBR to below 0.4 in 10 cases, indicating that AKBR rapidly reflects the intraoperative metabolic insults imposed on the liver. After the completion of operation, AKBR's returned to the normal value of above 0.7 in cases without cirrhosis. In contrast, 4 of 5 cases with cirrhosis exhibited delayed recovery of AKBR(p=0.053). The mean value of ICG R15 in the delayed recovery group of serial AKBR was 14.7%, significantly lower than 8.0% in the rapid recovery group(p=0.031). It seems that postoperative restoration of liver function in patients with poor hepatic functional reserve takes more time, as reflected in delayed recovery of AKBR. Changes in AKBR during and after liver transplantation were as follows: reduction to below 0.4 during anhepatic phase; recovery to above 0.4 concomitant with functioning of the new liver; maintenance at over 0.7 during the first week after the operation. Such findings were useful in monitoring the function of the grafted liver during the critical perioperative period.