It is generally accepted that the bile acids are responsible for pathologies as a result of deficiency or by toxic action. Quantitative deficiency is difficult to evaluate but the normal pool of bile acids is generally considered to be between 2 and4 grams. Daily loss and replacement by synthesis is thought to be between 500 and 700 mg. There is experimental evidence to demonstrate the toxic action of certain bile acids on metabolic structures and processes. There is no doubt that alterations in the metabolism of bile acids give rise to certain pathologic aspects in some diseases of the gastrointestinal tract or the hepatobiliary system. There are other conditions, on the other hand, in which the study of these acids may reveal significant physiopathologic implications. The first group includes terminal ileopathy, blind loop syndrome, gastric ulcer, gastritis, cholestasis, cirrhosis of the liver, and cholelithiasis. In the second group are such diverse conditions as acute pancreatitis, cancer of the colon, endocrine disturbances, some hyperlipidemias, and others. Much of the present day understanding of the physiopathology of the bile acids will probably have to be revised in the nex few years, in view of the rapid advances being made in this field.