The amount of bile acid excreted via an ileostomy at the end of the ileum should give an estimate of the amount of bile acid transported to the colon. In the present study, 8 patients with ileostomies at the end of the ileum but without disease or resection of the small intestine excreted 1690 +/- 205 mumol/day (mean +/- SEM) of bile acids from the ileostomies. In comparison with duodenal bile, cholic acid was increased at the end of the ileum and chenodeoxycholic acid decreased; in addition, bile acid sulfates were increased and bile acid glucuronides were decreased. When ursodeoxycholic acid, a bile acid that decreases biliary cholesterol saturation and dissolves gallstones, was administered at a dose of 500 mg to each subject, 59% +/- 8% (mean +/- SEM) of this bile acid was excreted within 24 h from the ileostomies. It is apparent from these studies that absorption of ursodeoxycholic acid from the small intestine is slower than previously anticipated and involves the entire small intestine and probably also the colon.