A series of 80 colorectal adenocarcinomas were analyzed immunohistochemically for the antigen recognized by a new monoclonal antibody (MCA) 47D10. These antigens are part of a complex family of substances similar to, yet distinct from carcinoembryonic antigen (CEA), and are termed nonspecific cross-reacting antigens (NCA). Formalin-fixed paraffin-embedded sections of colorectal adenocarcinomas were evaluated for the expression of these antigens and compared to the expression of CEA. Our study shows that 83.8% of the cases were positively stained for NCA while 91.3% were positive for CEA. Both antigens were coexpressed in 80% of the cases. No correlation was found between MCA 47D10 immunoreactivity and tumor grade, stage, size or location within the colon. In 25 cases, the benign colonic mucosa adjacent to the carcinoma stained positively with MCA 47D10. Normal colon does not express NCA as recognized by MCA 47D10, except in rare cells. Forty-eight of these cases had serum available for study. Both NCA and CEA were determined in these serum samples. Forty-two of these sera demonstrated elevated CEA levels, whereas only 8 showed increased levels of the 47D10 antigen(s). These findings suggest that the gene product(s) recognized by MCA 47D10 can be independently expressed or, more commonly, coexpressed with CEA in these tissues.