Ursodeoxycholic acid was administered to a patient with benign recurrent intrahepatic cholestasis to prevent cholestatic episodes. A detailed study of bile acid metabolism in this patient was carried out in the anicteric and icteric phases before and after ursodeoxycholic acid (750 mg/day) administration. Urinary, biliary and serum bile acids were measured by gas chromatography-mass spectrometry and by high-performance liquid chromatography techniques. During the anicteric phase the daily urinary excretion and serum concentrations of bile acids were within normal ranges, indicating normal hepatic uptake and secretion of bile acids during the cholestasis-free period. Only slight qualitative differences from normal individuals were observed; the relative proportions of deoxycholic acid in the bile and serum were higher, and 12-oxo-lithocholic acid was the predominant urinary bile acid. During the icteric phase a marked increase in the urinary excretion of primary bile acids and C-1, C-2, C-4 and C-6 hydroxylated metabolites was found. Serum bile acid concentrations increased before the rise in bilirubin, suggesting an acute disturbance in bile acid transport at the onset of the cholestatic attack. After ursodeoxycholic acid administration in the anicteric phase, bile became enriched with the exogenous bile acid, but little qualitative change was found in the other metabolites present in the urine, serum or bile during the anicteric or icteric phases. Prolonged administration of ursodeoxycholic acid failed to prevent recurrence of a cholestatic episode, suggesting that in benign recurrent intrahepatic cholestasis, oral ursodeoxycholic acid may be of little benefit in the treatment or prevention of cholestasis despite marked enrichment of the bile acid pool with this hydrophilic bile acid.