Mucins are heavily glycosylated glycoproteins which exhibit a variety of antigenic determinants consisting of carbohydrates and/or peptide sequences. The application of monoclonal antibodies and lectins in immunohistochemistry resulted in a considerable extension of knowledge regarding their topography during histogenesis. Additionally, typical alterations of antigenic profiles during neoplastic transformation of cells and tissues were described. A number of new results are in keeping with the assumption that mucin-associated antigens play an important role in tumor biology, for example metastasis, and as markers of prognosis. The purpose of the present paper is to give a review, including the authors' own results, of knowledge on the gastro-intestinal mucin antigens in experimental and clinical pathology.