We treated 30 patients with radiolucent gallstones with chenodeoxycholic acid (CDCA) or ursodeoxycholic acid (UDCA) at daily dosages of 300 to 600 mg. Duration of treatment ranged from 5 to 16 months. Gallstone dissolution was noted in 23.3% of the group. CDCA was effective in 22.2%, and UDCA was effective in 25%. Treatment with these bile acids was usually effective when radiolucent stones smaller than 5 mm in diameter were found in the normally functioning gallbladder. Improvement of symptoms was noted in 60.9% of the patients who had symptoms related to biliary disease prior to the treatment. There was no definite evidence of hepatotoxicity due to these bile acids, although transient elevation of transaminase activity of unknown clinical significance was observed in 36.7% of the patients during the course of treatment. Five patients (16.7%) experienced diarrhea during treatment, but it was transient as long as the dose remained at 300 mg daily. Our experience with UDCA revealed comparative efficacy to that of CDCA, and side effects were rare. Long-term low-dose therapy with CDCA or UDCA seems to be an effective and safe treatment for radiolucent gallstones.