Bile acids are supposed to promote colonic cancer. In Crohn's disease, colonic carcinomas are relatively rare. We, therefore, compared ileal and right colonic mucosal bile acids analysed by gas-liquid chromatography in 8 patients with ileal Crohn's disease (14-48 yrs.) and 7 patients with right colonic carcinoma (28-77 yrs.) who underwent surgery. In both ileal and colonic mucosa, nonsulphated bile acid concentrations were somewhat higher in Crohn's disease (20.98 micrograms/g +/- 4.77 SEM; 12.09 micrograms/g +/- 2.55) than in colonic carcinoma (16.06 micrograms/g +/- 3.46; 7.75 micrograms/g +/- 4.28). In ileal mucosa, percentages of lithocholic and deoxycholic acids were slightly higher in colonic carcinoma (3.9%; 23.2%) than in Crohn's disease (1.1%; 14.9%). In colonic mucosa, carcinoma patients had more lithocholic (7.6%) and less deoxycholic acid (11.9%) than patients with Crohn's disease (1.7%; 20.3%). Bile acid sulphate esters were similar in both diseases (ca. 3.0 micrograms/g in ileal, 1.4 micrograms/g in colonic mucosa). Our results show that ileal and right colonic mucosal nonsulphated bile acids tend to be even lower in right colonic carcinoma than in Crohn's disease. This agrees well with our earlier findings of low mucosal bile acid concentrations in patients with left colonic carcinoma (Tokai J Exp Clin Med 8: 59-69, 1983) and does not support the assumption that bile acids are envolved in right colonic carcinogenesis.