The mucus secretions of the oral, pulmonary and GI tracts of higher animals contain high molecular weight glycoproteins, some of which have been highly purified and characterized. They appear to be part of the general immunological system and include components responsible for blood-group specificity, which are known to be related to the red blood cell surface antigens. Colonic mucus glycoproteins have received very little prior attention. The present work is devised to determine the basic nature of the colonic mucus glycoproteins of human and hamster colonic tissue. Their composition and immunological reactions will be compared with the corresponding substances derived from human and hamster cancerous tissue. Similar comparisons will also be made of the corresponding plasma membrane glycoproteins isolated from tissue suspensions of normal and cancerous material. Variations, especially in the transglycosylases, but also in the core proteins, will be studied for normal and cancerous tissue of the two species.