The effects of ursodeoxycholic acid (UDCA, 750-1250 mg/day) were evaluated prospectively in 15 patients with primary sclerosing cholangitis (PSC). Five patients had associated inflammatory bowel disease. After 6 months of treatment, the proportion of patients suffering from fatigue or pruritus decreased from 60% to 20% and from 33% to 20%, respectively. No exacerbation of associated disorders was observed. Serum alkaline phosphatase levels (normal less than 100 IU/l) decreased from 401 +/- 53 to 222 +/- 42 (mean +/- S.E.; p less than 0.001), those of gamma-glutamyl transpeptidase, (normal less than 40 IU/l) from 520 +/- 89 to 185 +/- 32 (p less than 0.001) and those of alanine aminotransferases, (normal less than 30 IU/l) from 79 +/- 12 to 42 +/- 6 (p less than 0.02). In three patients, the discontinuation of UDCA was associated with an aggravation of the liver test results. In conclusion, this study shows that 6 months of treatment with UDCA leads to clinical and biochemical improvements in patients with PSC. These results suggest that UDCA could be an effective treatment for PSC, and may justify a controlled therapeutic trial.