Increased excretion and intestinal bacterial metabolism of bile acids and neutral sterols have been suggested to be associated with an increased risk of colorectal cancer. We determined fecal neutral sterol and bile acid profiles by new capillary column gas-liquid chromatographic methods in 18 patients with colorectal cancer, 10 omnivores, and 10 vegetarians. The methods also determine concentrations of esterified neutral sterols and saponifiable bile acids formed by intestinal bacterial action. Patients with colorectal cancer had the highest concentrations of neutral animal sterols, the lowest degree of esterification of neutral sterols, the lowest relative amount of saponifiable bile acids, and the highest concentrations of unconjugated primary bile acids. These differences were statistically significant (p less than 0.05) and more profound when the patients were compared with vegetarians than with omnivores. Since epidemiologic studies suggest that vegetarians have a lower risk of colorectal cancer than omnivores, these differences are discussed as possible risk factors for colorectal cancer.