Surgical specimens from 2 patients with chronic ulcerative colitis accompanied with colon cancer were evaluated by immunoperoxidative staining using monoclonal antibodies A7 (against human colon cancer), S202 (against human gastric cancer), and anti-carcinoembryonic antigen (CEA). The three monoclonal antibodies were reactive with cancerous tissue, anti-CEA antibody and monoclonal antibody S202 reacted with dysplasia tissues, whereas monoclonal antibody A7 did not. Using high-iron diamine technique for mucosubstances (sialomucin and sulfomucin), cancer and dysplasia showed no secretory elements. Surrounding mucosa showed both sialomucin and sulfomucin secretion.