The effects of enteral administration of various bile salts on bile output were investigated in the rat. After intraduodenal administration, all bile salts significantly increased bile flow and total bile output. Dehydrocholate had the greatest effect on bile flow. Cholate was next in degree of effectiveness followed by taurocholate, deoxycholate, and taurodeoxycholate. Bile output was significantly lower after ileal or gastric intubation of sodium dehydrocholate or taurocholate than after duodenal administration of these compounds. Conjugation of the bile salts tended to depress the overall effect on bile flow. These effects are discussed in terms of possible differences in the absorption of conjugated and unconjugated bile salts. Comparison of the effects of sodium dehydrocholate and taurocholate after intraduodenal and intravenous or intraperitoneal administration suggests that absorption rate or efficiency of absorption markedly influences the intensity of apparent choleretic activity. A relationship was observed between the structure of the bile salt and bile flow stimulation: the triketo form was more effective than the trihydroxy form and that, in turn, was more effective than the dihydroxy form. This is difficult to explain in terms of differences in absorbability but is consistent with a choleresis mechanism involving osmotic pressure effects. At a dose of 100 µmoles, in the rat, dehydrocholate does not function simply as a hydrocholeretic agent. Nevertheless, on the basis of the relative amount (percent) of solids in stimulated bile, there are clear differences in the nature of the choleretic activity of dehydrocholate and cholate