The prognosis of operated biliary atresia in the cases with bile excretion chiefly depends upon the prevention of ascending cholangitis. An antibiotic is therefore intravenously administered during the early postoperative phase, but cannot be used over a long period. In the cases showing satisfactory bile excretion after operation, ascending cholangitis is rare because of rapid disappearance of jaundice. Regarding this, the authors prescribed ursodeoxycholic acid (UDCA) at 10-15 mg/kg/day to 6 infants with biliary atresia for several weeks after operation, and then determined the effects of UDCA in improving jaundice and bile excretion. As a result, serum bilirubin and serum total bile acid (STBA) levels were decreased in 4 of the 6 infants. In the remaining 2 infants, their STBA levels showed no decrease, but were rather increased; these infants subsequently died of hepatic failure. These results suggested that UDCA is useful in the treatment of cholestasis associated with biliary atresia in the cases attaining postoperative bile excretion. It was also suggested that the treatment with UDCA should be stopped when the STBA levels increased after the beginning of the treatment. Therefore, it was thought that STBA levels measured during UDCA therapy could serve as a good indicator of the choleretic effect of UDCA.