The effect of administration of primary and secondary bile acids on absorption of cholesterol was investigated in 15 volunteers. Eight Caucasians with radiolucent gallstones were studied before and after administration of chenodeoxycholic acid (all eight) and cholic acid (eight before, six after treatment) for 3 months, and seven healthy subjects were studied before and five were studied after administration of deoxycholic acid for 6 weeks. The hourly absorption of [3H]cholesterol was measured for 24 hours in a 20-cm duodenal segment by use of an intestinal perfusion technique. Fasting serum cholesterol and triglyceride levels were also measured before and after administration of bile acid. In patients with gallstones, absorption of cholesterol in the duodenum, expressed as the mean (+/- SEM) percentage of [3H]cholesterol absorbed hourly for 24 hours, was not significantly different after administration of chenodeoxycholic (22.5 +/- 4.4%) or cholic (25.6 +/- 5.9%) acid when compared with the pretreatment value (21.1 +/- 4.3%). Moreover, administration of chenodeoxycholic and cholic acid did not affect serum lipid levels. In contrast, administration of deoxycholic acid to healthy volunteers suppressed [3H]cholesterol absorption (13.2 +/- 3.2%) compared with that of the pretreatment period (26.5 +/- 3.8%) and decreased serum cholesterol levels by 15%. Our results suggest that chenodeoxycholic acid decreases the concentration of cholesterol in bile and dissolves gallstones by a mechanism other than inhibition of absorption of cholesterol. The data also indicate that the hypocholesterolemic effect of deoxycholic acid is due to the inhibition of intestinal absorption of cholesterol.