AbstractSignificant correlations have been reported by epidemiologists between the mortality from colorectal cancer in various populations and the consumption of meat or lipids by these populations. These have directed considerable attention to possible relationships between diet and the occurrence of this neoplasm. We have carried out studies of the composition of bile from rats as influenced by diets of varying lipid content. Two cannulas were surgically implanted to form an externalized bile duct through which bile was drained from the common duct and returned to the duodenum. Small aliquots were analyzed for total bile acids by enzymatic assay and for individual bile acids by high‐pressure liquid chromatography, gas chromatography and gas chromatography‐mass spectrometry. Animals consuming diets highest in lipid content provided bile with the greatest amounts of bile acids. The primary bile acids, taurocholic, taurochenodeoxycholic, and tauro α‐ and β‐muricholic acids made up more than 99% of the 3α‐hydroxy bile acids and were found in approximate molar ratio of 2∶1∶1. Either complete drainage of bile without return to the duodenum, or biliary tract obstruction had pronounced influence on the rate of secretion of bile and its composition.