Fasting and postprandial gallbladder volumes have been measured by sonography both in healthy subjects and gallstone patients ingesting: (a) tauroursodeoxycholic acid; (b) ursodeoxycholic acid; (c) placebo. Each bile salt was given at a dose of 10 mg kg-1. Sonography was repeated in gallstone patients fed tauroursodeoxycholic acid or ursodeoxycholic acid (10 mg kg-1 day-1) for 1 month. Gallstone patients had gallbladder stasis (increase in fasting and residual volumes) and decreased postprandial emptying. Acute ingestion of tauroursodeoxycholic acid or ursodeoxycholic acid did not modify postprandial gallbladder emptying in both groups of subjects. After one month's therapy with tauroursodeoxycholic acid or ursodeoxycholic acid, fasting gallbladder volume further increased in gallstone patients, although gallbladder emptying remained unchanged. Thus, therapeutic doses of tauroursodeoxycholic acid or ursodeoxycholic acid do not acutely modify postprandial gallbladder emptying in either healthy subjects or gallstone patients. Chronic treatment with either bile salts results in an increase in fasting gallbladder volume without interfering with the extent of postprandial gallbladder emptying.