Ursodeoxycholic acid administration has been reported to improve cholestasis and inflammatory activity in primary biliary cirrhosis and, in an uncontrolled study, also in young adults with cystic fibrosis (CF) and chronic cholestasis. As an improvement in nutritional status was also observed in these young adult patients, we investigated whether the administration of a medium dose of ursodeoxycholic acid ameliorates the nutritional status of malnourished young adult CF patients with chronic liver disease. The study included 51 patients (27 male patients and 24 female patients; age range, 8-32 years; median, 14) with body mass percentiles < 90%. Patients were randomly assigned to receive either ursodeoxycholic acid (10-12 mg/kg/day) alone or with taurine (18-22 mg/kg/day). Patients were followed in a crossover fashion within each group; 6 months of treatment was randomly alternated with 6 months of placebo. Nine patients dropped out before concluding the study. Liver function tests, nutritional status, and coefficients of fat absorption were determined at entry and after each 6 months of placebo or treatment. Nutritional status and fat absorption were not significantly modified by either treatment. Liver function tests improved after ursodeoxycholic acid administration only in patients with concomitant chronic liver disease. Our findings indicate that 6 months of therapy with a medium dose of ursodeoxycholic acid, either alone or with taurine, does not improve the nutritional status of young malnourished CF patients. Higher doses given for longer periods might be worth investigating.