Samples of colorectal carcinoma, adenoma and normal colorectal mucosa were examined for the expression of TGF-beta by immunohistochemistry. Immunoreactivity for TGF-beta was present in 52 out of a total of 58 samples of normal mucosa examined. In adenomas and carcinomas TGF-beta expression was observed in eight out of ten and 46 out of 48 samples respectively and was largely restricted to epithelial cells. In normal mucosa differential expression of TGF-beta was present within epithelial cells, those in the upper parts of the crypts showing enhanced immunoreactivity compared to cells in the proliferative compartment. This pattern of differential staining is consistent with TGF-beta having an important role in the control of growth and differentiation in colonic mucosa.