Patients (134) with radiolucent gallstones were randomly allocated to receive either placebo or 1 of 3 different doses of chenodeoxycholic acid (CDCA); 750, 1500 or 3000 mg). The initial dose was lowered if not well tolerated. In 107 patients who were treated for more than 3 mo., stones dissolved in 21 and were smaller in 25 patients. Partial or complete dissolution occurred in 4 of the 13 receiving 375 mg/day, 14 of 37 receiving 750 mg, 24 of the 38 receiving 1500 mg and 4 of 8 receiving 3000 mg/day. The number of responders to the therapy was significantly greater in the groups of patients receiving 1500 mg/day or 17-24 mg/kg body weight than in any other group. Side effects, i.e., diarrhea and transaminase increase, are also dose related. The optimal dose of CDCA may be between 17 and 20 mg/kg body weight.