Out of 95 patients with radiolucent gallstones who enrolled in a clinical study with chenodeoxycholic acid (CDC) for gallstone dissolution 75 patients with cholecystolithiasis completed 12 months of treatment. As a side effect 31% of patients reported intermittent diarrhea which did not cause cessation of therapy or missing of work. The incidence of biliary colic was markedly decreased during treatment in comparison to the rate in the year before. From more than 20 laboratory values checked before start and every 3 months during therapy only aminotransferases increased up to 3 fold in 20% of patients. gamma-GT elevated in 31% of patients before treatment improved in half of these patients during therapy. Gallstone dissolution defined as 30% or more diminution of the gallstone area on comparable x-rays occurred in 40% of patients. Analysis of factors showed that gallstones above 2 cm in diameter did not dissolve. When the dose of CDC was retrospectively related to body weight a success rate of 68% was found in the group taking more than 13 mg CDC/kg/day. The lithogenic index determined at 6 and 12 months had significantly decreased after 6 months in patients with success. This study demonstrates that medical dissolution of gallstones with chenodeoxycholic acid should be performed in patients with radiolucent stones of less than 2 cm in diameter and with a dose above 13 mg CDC/kg body weight/day. Under these conditions the success rate is above 60% accompanied by minimal side effects.