Sections of normal colon, adenomas, and adenocarcinomas were examined by immunohistochemistry for the expression of c-erbB-2 proto-oncogene product in order to assess its potential diagnostic value in predicting the malignant potential of these lesions. We compared the degree of epithelial abnormality and clinical parameters, including Dukes' classification and survival time with the extent of immunoperoxidase staining. Sections of normal colon and tubular adenomas examined demonstrated a weak immunostaining localized to the luminal surface cells. However, higher level of c-erbB-2 expression was observed in dysplastic areas of one tubular and one villous adenoma. Out of 40 adenocarcinomas, only 2 samples showed weak immunoreaction, while 38 samples were moderately or strongly positive for c-erbB-2 protein. The intensity of staining correlated positively with the stage of disease and postoperative survival time.