In a dose-response study, a formulation of chenodeoxycholic acid (chenic acid) with complete bioavailability was fed at doses of 0, 250, 500, 750 mg for randomized 6-week periods to 13 patients with radiolucent gallstones. The proportion of chenic acid in biliary bile acids increased in direct relation to dose. Lithocholic acid also increased, but ursodeoxycholic acid showed no significant change. Bile saturation decreased with increasing dose, but response was variable and achieved significance only at 750 mg/day. Cholesterol saturation was negatively correlated with the proportion of chenic acid in biliary bile acids: When biliary bile acids contained greater than 70% chenic acid (and ursodeoxycholic acid), bile became unsaturated, on the average. The data suggest that a dose of at least 10-15 mg/kg may be necessary to obtain desaturation in many gallstone patients.