To detect an early colon carcinoma in its stage of carcinoma in situ, colonoscopic examinations with removal of all adenomas of the left colon (particularly of the sigmoid tract and rectum), followed by histological and biochemical evaluations, have been performed on 30 patients. Two-thirds of the adenomas examined presented histological patterns of tubular, tubulovillous, and villous adenomas; those with moderate or severe dysplasia were at high risk of neoplastic transformation. Measurement of estradiol (ER) and progesterone (PR) receptors was performed in the cytosol and in the nuclei of solitary and multiple adenomas and in those with synchronous carcinomas using the dextran-coated-charcoal (DCC) method. Steroid receptors were usually found in the cytosol of the large polyps of male rather than female patients (46% vs 11%) and in the cytosol of the adenomas with moderate or severe dysplasia in male patients. Malignant lesions usually possessed both ER and PR in the cytosol and nuclear fraction. These findings led to hypothesize that patients with adenomas of the colorectal tract with moderate or severe dysplasia and nuclear steroid receptors should be considered at high risk for colon carcinoma and therefore need a special follow-up program.