Methods of morphological, histochemical and immunohistochemical analyses were used to further characterize differences between tumorous and adjacent grossly normal tissues in chemically-induced colon cancer in rats. Colon tumors were induced by the treatment of rats with 1,2-dimethylhydrazine or with N-methyl-N’-nitro-N-nitrosoguanidine alone or with subsequent treatment with deoxycholic bile acid. Tissues were studied morphologically (for the presence of goblet cells in the colon crypts, and the extent of infiltration of lymphocytes into the crypts and between them) histochemically (for the presence of positive reaction to neutral and acid mucopolysaccharides) and immunohistochemically (for the presence of tissue polypeptide antigen). All data were evaluated quantitatively, and index of tissue damage was calculated for both tumorous and non-tumorous tissues. Significant morphological differences were found between tumorous and adjacent apparently normal tissue. Histochemically and immunohistochemically, both types of tissue reacted very similarly to exposure to the carcinogens. Index of damage was significantly different from normal untreated colon in both kinds of tissue. It was suggested that precancerous state in tissue adjacent-to-tumor could be detected using the combination of these method