134 patients with radiolucent gallstones were randomly allocated to receive either placebo or 1 of 3 different doses of chenodeoxycholic acid (CDCA); 750, 1,500, or 3,000 mg). The initial dose was lowered if not well tolerated. 107 patients were treated for more than 3 months. Among them, 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 1,500 mg and 4 of 8 receiving 3 000 mg/day. The number of responders to the therapy was significantly greater in the groups of patients receiving 1,500 mg/day or 17–24 mg/kg body weight than in any other group. However, side effects, i.e., diarrhea and transaminase increase, are also dose related. It appears from this study that the optimal dose of CDCA may be between 17 and 20 mg/kg body weigh