['The functional recovery of the remnant liver after an extended hepatectomy is critical for the outcome of the patient. The aim of this prospective study was to examine whether biliary bile acids could be an indicator for postoperative liver function.', 'Externally drained bile samples were obtained from 51 patients with biliary or periampullary carcinomas before and after surgery. Patients were categorized into 3 groups: group A, 29 hepatectomized patients without liver failure; group B, 7 hepatectomized patients with liver failure (maximum serum bilirubin level, >10 mg/dL); and group C, 15 patients who underwent biliopancreatic resection without hepatectomy, with a good postoperative course. Bile samples were withdrawn 1 day before surgery and on postoperative days 1, 2, 3, 4, 6, and 7. Total bile acids were measured with a 3 alpha-hydroxysteroid dehydrogenase method.', 'Before surgery, the concentration of bile acids was higher in groups A and C than in group B, and correlated significantly with the indocyamine green disappearance rate (KICG) values (R(2) = 0.557; P <.0001). After surgery, bile acid concentrations decreased in all 3 groups until postoperative day 2, which was followed by a gradual increase. The concentration recovered to the preoperative level in groups A and C but remained low in group B. Biliary bile acid concentrations on day 2 correlated significantly with remnant liver KICG values (R(2) = 0.257; P =.0019). Among several parameters studied, including KICG, remnant liver KICG, biliary bile acids, and biliary bilirubin, biliary bile acid concentration had the most predictive power for occurrence of postoperative liver failure.'] Is biliary bile acid concentration a simple and reliable indicator for liver function after hepatobiliary resection for biliary cancer?