In this necroscopy study the relation between carriage and size of colorectal polyps was correlated with luminal steroid concentrations in respect to malignant risk. Of the 92 subjects entered into the study, 68 had adenomatous polyps of the large bowel, of which 19 had adenomas > 0.9 cm in diameter (large adenomas), 26 in the range 0.5–0.9 cm in diameter (medium adenomas) and 23 of 0.4 cm or less in diameter (small adenomas). Sixty-three percent of subjects carrying large adenomas and 26% of persons carrying small adenomas had an abnormal ratio (> 1.0) of lithocholic acid to deoxycholic acid in intestinal contents as compared to 17% of the adenoma-free comparison group (n= 24). These findings support the suggestion that the ratio of lithocholic acid to deoxycholic acid as a faecal marker may be a useful adjunct to screening procedures for colorectal cancer.