Bile acids are believed to play a role in the etiology of colorectal cancer. To investigate a possible relationship between bile acids and colorectal tumors, duodenal bile acids were analyzed in 18 patients with colorectal adenomas, 18 patients with colorectal carcinoma and 18 control subjects. Using high performance liquid chromatography and immobilized 3 alpha-hydroxysteroid dehydrogenase in column form, significant increases in the proportion of chenodeoxycholic acid and significant decreases in the proportion of deoxycholic acid and lithocholic acid were found in the bile of patients with colorectal adenoma or carcinoma compared with the control subjects. The data support the concept that bile acids have a role to play in the development of large bowel tumors.