Progress in research on bile acid metabolism has been accelerated by new sensitive methods for detecting individual bile acids in biologic fluids. The most important advances involve the pathophysiologic basis for formation of cholesterol gallstones, the disturbed secretion and synthesis of bile acids in cholestasis and liver disease, and the malabsorption and deconjugation of bile acids. As a result a rational basis for treatment has been made possible, for example the dissolution of cholesterol gallstones with chenodeoxycholic acid and ursodeoxycholic acid or the treatment of bile acid malabsorption syndromes with cholestyramine and medium-chain triglycerides. However, despite the substantial progess made in the past few years, many challenges remain for investigators in the area of the pathophysiology of the biliary circulation. One of these challenges is the possibility that altered bile acid metabolism contributes to the patho-genesis of colon cancer in developing countries.