The properties of a specific transport system for bile salts, which is located in the ileum of the small intestine are described. The system operates by a sodium ion cotransport mechanism, and it functions in maintaining a normal enterohepatic circulation of bile salts. Analysis of structure-activity data allows us to depict our hypothesis for the interaction of bile salt and Na with the membranal recognition site of this transport system. The sequellae of metabolic disorders which can arise following disease or surgical ablation of the ileal region of the intestine which result in an interrupted bile salt enterohepatic circulation are described. We suggest that these findings hold interest to toxicologists, since it is not beyond reason that toxic agents might exist which impair the function of this transport system specifically or which could poison the ileal mucosal cell. Such agents might be detected by the presence of some of the described metabolic disorders. Finally, we discuss the ileal transport of the sulfated esters of bile salts and the possibility that this might relate to that aspect of detoxification pertaining to their enhanced excretion.