The excretion of D-glucaric acid (DGA), a metabolite of the cytochrome P-450 pathway, is considered a marker of the viability of hepatocytes. Twelve cases of biliary atresia (BA) have been investigated, correlating the level of DGA, degree of histological alteration of liver parenchyma, and clinical outcome. Urine was collected in the preoperative period. Five patients had good bile flow after the Kasai operation and demonstrated mild liver fibrosis. The urine excretion level of DGA in this group was 17.2 +/- 3.1 mumol/d (control, 15.2 + 2.2 [67od] mmol/d). Seven patients had partial bile drainage or prolonged jaundice. They also had altered liver parenchyma and a very low level of DGA in the urine preoperatively (4.2 + 2.2 mumol/d). Urine excretion of DGA reflected the degree of alteration of liver parenchyma and closely correlated with clinical outcome. Measurement of DGA before the Kasai operation provides information concerning the present hepatic function and the postoperative prognosis. Once the activity of hepatocytes deteriorates, this test is quicker than the other liver function tests. It is noninvasive and is a useful clinical prognostic predictor in BA.