A multi-center double-blind controlled trial of ursodeoxycholic acid (UDCA) for treatment of primary biliary cirrhosis (PBC) was carried out. Twenty two and 23 patients were treated with 600 mg/day UDCA and placebo, respectively, for 24 weeks. In UDCA-treated patients, fall of serum aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase and gamma-glutamyltranspeptidase activities started within 4 weeks after start of the trial and continued throughout the trial period. The serum IgM level fell in 7 UDCA-treated patients examined but not in 10 placebo-treated patients examined. Serum bilirubin concentration showed no significant change at the end of the study in either of UDCA- and placebo-treated group of patients. There was no significant difference between these two groups with respect to the frequency of improvement of pruritus. In UDCA-treated patients, serum bile acid composition changed markedly, though its concentration showed no significant change. The percentage of total bile acid which ursodeoxycholic acid took up increased, whereas those which cholic acid, chenodeoxycholic acid and deoxycholic acid took up were decreased.