Liver disease is increasingly recognized as a major cause of morbidity in cystic fibrosis (CF). Preliminary data suggest that ursodeoxycholic acid (UDCA) may be beneficial for treatment of this manifestation. We performed a double-blind, multicenter trial in these patients to establish efficacy and safety of UDCA in terms of the improvement of clinical and nutritional indicators besides standard liver function tests. We also intended to establish whether taurine supplementation has a beneficial effect in patients receiving UDCA. From June to December 1990, we enrolled in 12 centers 55 CF patients with liver disease (39 male subjects; median age, 13.8 years). They were randomly assigned to receive for 1 year one of the following treatments: UDCA (15 mg/kg body weight daily) plus taurine (30 mg/kg body weight daily), UDCA plus placebo, placebo plus taurine, or double placebo. Clinical and laboratory evaluations were performed every 3 months. After 1 year, deterioration of overall clinical conditions, as indicated by the Shwachman-Kulczycki score (SKS), occurred in patients who received placebo but not in those who received UDCA (P = .025). Patients treated with UDCA also showed an improvement in gamma-glutamyl transpeptidase (GGT) (P = .004) and 5'-nucleotidase (P = .006) levels. Treatment with taurine was followed by a significant increase in serum prealbumin levels (P = .053), a trend toward a reduction in fat malabsorption, and no effect on the biochemical profile. No severe side effects occurred with any treatment. Thus, we concluded that UDCA administration improves clinical and biochemical parameters in CF patients with liver disease. Taurine supplementation may be indicated in patients with severe pancreatic insufficiency and poor nutritional status.