One hundred and twenty-six patients with radiolucent gallstones in 'functioning' gallbladders were treated with 8-10 mg ursodeoxycholic acid (UDCA) kg/day and followed to a treatment conclusion. Complete or partial gallstone dissolution was achieved in 74 (59 per cent). However, only 22 achieved complete gallstone dissolution, as judged by two normal oral cholecystograms; ultrasonograms were performed in 16 of these patients, and all were normal. UDCA was stopped in 76 patients: because of cystic duct obstruction (n = 12), severe biliary pain (n = 13), non-response (n = 25) or partial stone dissolution with arrested progress (n = 26). Life-table analysis showed that complete gallstone dissolution rates at four years were 25-30 per cent (two normal oral cholecystograms) and 17-19 per cent (two normal oral cholecystograms plus one ultrasonogram). All patients with complete gallstone dissolution had shown partial stone dissolution at 6-12 months; of those with partial stone dissolution at six months, only 25 per cent went on to complete gallstone dissolution, and then always within two years. Efficacy correlated inversely with stone size but not with age, sex, obesity or on-treatment saturation indices. Acquired surface gallstone calcification developed in 13 patients (life-table analysis 22 +/- 7 per cent at four years); none of these patients achieved complete gallstone dissolution and only five achieved partial stone dissolution. Thus, despite relatively high partial gallstone dissolution rates, the ultimate efficacy of UDCA in achieving complete gallstone dissolution is low.