We conducted a study to measure the individual fractions of bile acids contained in the serum and bile for a period of 20 days starting on the day of surgery as parameters for evaluating prognosis following hepatectomy. 21 patients undergone hepatectomy were divided into 14 patients who demonstrated uneventful progress and 7 cases fell in postoperative hepatic insufficiency. In addition, another 7 patients undergoing cholecystectomy were served as the control. In the cases which demonstrated uneventful progress following hepatectomy, serum bile acids primarily consisting of cholic acid (CA) transiently elevated to 10-20 μmol/l on the 3rd to 5th days following surgery, but returned to the normal range of 5 μmol/l or less on the 10th day. However, in those cases having a poor prognosis following hepatectomy, a rise in serum bile acids dominated by chendoeoxycholic acid (CDCA) was observed soon after surgery, with the proportion of CDCA to total bile acids (TBA), (CDCA/TBA), being in excess of 70%. In addition, similar trends were observed in regard to bile acids in bile. On the other hand, in the cholecystectomy group, there was no significant rise in TBA observed both before and after surgery and there was no change in the composition of bile acids. Based on the above, it is believed that by measuring the ratio of serum CDCA to TBA soon after hepatectomy (within 5 days), it is possible to estimate the prognosis.