We have previously demonstrated that there are two subgroups of patients with different types of biliary bile acid output after relief of obstructive jaundice by percutaneous transhepatic biliary drainage (PTBD). The reason for two groups is not clear but is possibly the difference in hepatic reserve function. The aim of this study was to examine the relation of biliary bile acid output to the hepatic ATP level and biliary excretion rate of indocyanine green (ICG) in humans. Patients whose bile could be collected through a PTBD tube participated in this study. The mean serum total bilirubin concentration was 12.7 mg/dl at the time of PTBD, decreasing to 1.1 mg/dl before surgery. These patients underwent curative resection for cancer of the bile duct, duodenal papilla, or pancreatic head after the relief of hyperbilirubinemia. Bile was collected at 1-hour intervals for 5 hours after intravenous administration of ICG (0.5 mg/kg) within a few days before surgery, and a small liver tissue sample was obtained immediately after laparotomy without using ischemic procedures. The concentrations of total bile acid and ICG in bile, the bile flow rate, and the bile acid output and ICG excretion rate in bile over 5 hours were determined. ATP concentrations in liver tissue were determined by high performance liquid chromatography. Results of hepatic ATP levels were correlated with the bile acid output and ICG excretion rate into bile. Both the biliary bile acid output (micromoles per 5 hours) and ICG excretion rate (percent of injected dose of ICG) over 5 hours were significantly correlated with the hepatic ATP level (p = 0.0190 and p = 0.0084, respectively). Neither the bile flow rate nor the serum liver function tests were related to the hepatic ATP level. Significant correlation was found between the bile acid output and the ICG excretion rate (p = 0.0127). Biliary bile acid output reflects the hepatic ATP level. Determination of the biliary bile acid output and ICG excretion may provide useful parameters for evaluating the hepatic energy status, which is essential for organ viability.