Recent clinical studies have indicated that ursodeoxycholic acid (ursodiol), administered at dosages ranging between 10 and 15 mg/kg/day, improves liver function indices in both cholestatic and inflammatory chronic liver diseases. These dosages would be considered high for the use of ursodiol in gallstone dissolution therapy. To investigate the dose-response relationship to ursodiol administration, we planned a few studies in patients with primary biliary cirrhosis (PBC), primary sclerosing cholangitis (PSC), and chronic hepatitis (CH). Patients with PBC were subdivided into two groups on the basis of their serum bilirubin values, with 2 mg/dl as the dividing line. Ursodiol was given at dosages of 250, 500, and 750 mg/day for consecutive periods of two months, the order of treatment being randomly assigned to each patient. The enrichment with ursodiol of biliary bile acids was similar in both PBC and CH and, within the PBC group, in both anicteric and icteric patients. Highly significant decreases in serum enzyme levels were observed in all groups with the 250 mg/day dose, corresponding to about 4-5 mg/kg/day. The two higher doses induced further improvements in serum enzyme levels, especially in patients with PBC, but no significant differences were found between the 500 and the 750 mg/day doses. The improvements were roughly proportional to the enrichment of conjugated biliary bile acids with ursodiol. Serum bilirubin levels, an important prognostic factor in PBC, were also significantly reduced by ursodiol administration in patients with initial serum levels higher than 2 mg/dl. The present study indicated that ursodiol is a potentially useful drug for chronic liver disease.(ABSTRACT TRUNCATED AT 250 WORDS)