It has been previously suggested that treatment with ursodeoxycholic acid leads to decreased gallbladder emptying. The proposed mechanism is decreased release of cholecystokinin through negative feedback control by an increased amount of intraduodenal bile acids. In the present study we examined cholecystokinin release and gallbladder contraction after oral administration of a commercial fatty meal (Sorbitract; Dagra, Diemen, The Netherlands) using ultrasonography in eight normal subjects and eight gallstone patients before and after 1 and 4 weeks of treatment with ursodeoxycholic acid (10 mg kg-1.day-1). Fasting gallbladder volume increased in 15 of 16 subjects during treatment (P less than 0.01). Minimal volume did not change. Therefore, both absolute and relative gallbladder emptying increased during therapy. Maximal decrement of gallbladder volume in milliliters and percentage as well as integrated gallbladder contraction during 90 minutes in milliliters and percentage were significantly increased after 1 and 4 weeks of treatment with ursodeoxycholic acid when compared with data before therapy. Gallstone patients tended to have larger fasting and residual gallbladder volumes than normal subjects, whereas parameters for the amount of bile expelled (maximal decrement of gallbladder volume and integrated gallbladder contraction in milliliters and percentage) did not differ. Release of cholecystokinin did not change during treatment and did not differ significantly between patients and normal subjects. Mean relative percentage of ursodeoxycholic acid in bile during treatment in 13 subjects consenting to have duodenal intubation was 47% (range 31%-60%). Changes of fasting gallbladder volume after institution of bile acid treatment correlated significantly (r = 0.74, P less than 0.01) with changes of cholesterol saturation index but not with relative percentage of ursodeoxycholic acid in bile. This study indicates that gallbladder emptying does not decrease during treatment with ursodeoxycholic acid. Moreover, there is no evidence of decreased cholecystokinin release.