Measurements of cholesterol absorption were performed by an intestinal perfusion technique before and after 4 wk of administration of three different dihydroxy bile acids [ursodeoxycholic acid (1 g/day), chenodeoxycholic acid (1 g/day), and deoxycholic acid (0.4 g/day)] in 6 normal volunteers. Mean hourly absorption of cholesterol declined from 41 mumol/h in the control period to 31 mumol/h (-22%) during feeding of chenodeoxycholic acid (NS). During deoxycholic acid administration, mean cholesterol absorption decreased from 46 to 28 mumol/h (-28%; p less than 0.05). Ursodeoxycholic acid feeding was associated with a reduction of cholesterol absorption from 38 to 13 mumol/h (-70%; p less than 0.05), even though the input of cholesterol from bile was reduced significantly (from 123 to 86 mumol/h). The results suggest that the hydroxy groups at different positions on the bile acid nucleus of these three dihydroxy bile acids differ in their potential for cholesterol absorption.