The relative conjugation of cholic acid with glycine and taurine (G : T ratio) was studied in duodenal fluid obtained from 13 patients with ileal disorders, 4 patients with disorders which involved the duodenojejunum primarily (2 with nontropical sprue and 2 with Whipple's disease), and 5 student volunteers. The enterohepatic recirculation of sodium taurocholate-24-14C was studied in all subjects, and the relative conjugation (G : T ratio) of deoxycholate-14C, derived from bacterial metabolism of the injected taurocholate-14C, was measured in appropriate duodenal samples. In selected experiments, unconjugated bile salts, cholic acid-14C and deoxycholic acid-14C, were each administered intravenously, and their relative conjugation (G : T ratio) was measured in duodenal samples obtained throughout an initial 3-hr period and serially thereafter. For both bile salts, the lowest G : T ratio exhibited by patients with a disorder of the ileum was higher than the highest G : T ratio observed in either student volunteers or patients with duodenojejunal disorders. These changes were related to the markedly decreased enterohepatic recirculation of injected taurocholate-14C and injected deoxycholate-14C in patients with ileal disorders. The G : T ratio of cholic acid-14C and deoxycholic acid-14C was elevated to comparable levels in duodenal fluid sampled throughout the 3-hr period following intravenous injection of these bile salts into patients with ileal disorders. Furthermore, serial determinations of G : T ratio for deoxycholate-14C were similar to initial values after injection of either deoxycholate-14C or taurocholate-14C. Thus, the hepatic origin of these altered G : T ratios has been demonstrated. Although the precise mechanism involved in the production of these changes was not determined, oral administration of taurine to patients with ileal disorders resulted in a marked decrease in G : T ratio, demonstrating a maintained capacity for conjugation with taurine. Patients with Whipple's disease exhibited G : T ratios for both bile salts which were intermediate between those of student volunteers and patients with nontropical sprue, on the one hand, and patients with ileal disorders on the other, decreasing to a normal range after treatment.