The effects of ursodeoxycholic acid (UDCA, 13-15 mg/kg body weight daily) were prospectively evaluated in fifteen patients with primary biliary cirrhosis (PBC). The mean concentration of UDCA in serum expressed as the percentage of total bile acids rose from 0% at baseline to 58% (SEM 9%) after 2 years' treatment, whereas total serum bile acid levels did not change significantly. The proportion of patients with pruritus necessitating the use of cholestyramine was significantly lower at 2 years than at baseline. Standard liver function tests improved in all the patients. At 2 years the average activities of gamma-glutamyltranspeptidase, alkaline phosphatases, and alanine aminotransferase and bilirubin levels were reduced (respectively 78%, 65%, 68%, and 36% of pretreatment values). In three patients who agreed to interrupt the ingestion of UDCA for 3 months after 2 years' treatment there was clear deterioration in liver function tests, which again improved after reinstitution of UDCA. These results suggest that long-term UDCA might be a safe and effective treatment for PBC, but a randomised, controlled, double-blind trial is urgently needed.