Through the use of a technique for raising monoclonal antibodies, coupled with a solid-phase radioimmunoassay utilizing immobilized glycopeptides prepared from the surface membranes of the colorectal cancer cells (LS 180) used for the immunization, carbohydrate-directed monoclonal antibodies were obtained. One of the monoclonal antibodies, MLS 102, reacted immunohistochemically intensely with the colorectal cancer cell surface and the mucinous glycoproteins secreted by the cancer cells, but only weakly with normal colon tissue. The antigenic determinant recognized by MLS 102 was the carbohydrate moiety of glycoproteins with terminal sialic acid. The antigens defined by other monoclonal antibodies, MLS 103 and 104, were immunohistochemically detected in both normal colonic epithelial and cancer cells. These antibodies seemed to recognize the carbohydrate moieties of both glycoproteins and glycolipids. The method described in this report can be generally applied to raise cell surface carbohydrate-directed antibodies.