The authors invrstigated whenther samll dose of ursodeoxycholic acif treatment influences biliary concentration, nucleation time and gallbladder empting. 3 patients with cholesferd gallstones receired 400 mg ursodeoxychilic acid per prior to cholecystectomy. Treatment with small dose of ursodeoxycholic acid decreased the gallbladder chlesterol saturation index and prolonged the nucleation time ,bur had no effect on gallbladder empyting. We bilieve that snall dose of ursodeoxyxholic acis mat prevent the gallstone formation by decreasing xholecterol saturation index and lengthening the nucleation time.