Fine structure and function are closely related in the cells of the different tissues. For this reason a comparative study combining histochemical techniques and scanning electron microscopy can result a potentially useful tool in the search for cell markers of preneoplastic stages of the colon mucosa. With this purpose, samples of normal colon mucosa, adenomatous polyps and adenocarcinomas obtained by colonoscopy were studied by histochemical techniques for the detection of epithelial mucosubstances and by scanning electron microscopy. Differences were shown in the architectural arrangement of the colon epithelium between the normal mucosa, the adenocarcinoma and the polyps studied, while between tubular an tubulovillous adenomas no marked differential ultrastructural features were found. Acid mucosubstances distribution pattern showed that sialomucin predominated in the colon mucosa harboring a carcinoma and in the tubulo-villous polyps as well as in the mucosa remote from adenocarcinoma and from the two cases of familial polyposis coli histologically considered as tubulo-villous adenomas. On the other hand tubular adenomas and normal mucosa showed a predominance of sulfomucin.