The expression of blood group antigens A, B, H, T-antigen and CEA was determined in tissue samples of polyps of the rectosigmoideum removed by endoscopic polypectomy. On average 39 months later, during colonoscopic examination bioptic samples were removed at the site of previous polypectomy and the expression of the same tumour markers as previously was determined. In contrast to literary data, the cellular expression of blood group antigens was demonstrated only in one case out of seven adenomas of the rectosigmoideum. On the other hand, cellular expression of blood group antigen B was found in 6 cases at the site of previous polypectomy and in 6 cases, this antigen was incompatible. Interpretation of these results is difficult at this time.