OBJECTIVE: Tumor-associated antigens may be expressed as surface glycoproteins. These molecules undergo qualitative and quantitative modifications during cell differentiation and malignant transformation. During malignant transformation, incomplete glycosylation is common, and certain glycosylation pathways are preferred. These antigens might help distinguish between ovarian and colonic adenocarcinomas in the primary and metastatic lesions. Different cytokeratins have been proposed as relatively organ-specific antigens. DESIGN: We used monoclonal antibodies against T1, Tn, sialosyl-Tn, B72.3, CA125, carcinoembryonic antigen, and cytokeratins 7 and 20 to detect tumor-associated glycoproteins and keratin proteins in ovarian and colonic carcinomas. RESULTS: CA125, carcinoembryonic antigen, and cytokeratins 7 and 20 can distinguish between colonic and serous or endometrioid adenocarcinomas of the ovary in both primary and metastatic lesions. Mucinous ovarian adenocarcinomas differed in that they express carcinoembryonic antigen and cytokeratins 7 and 20 and weakly express CA125. The other glycoprotein antigens were equally expressed by ovarian and colonic adenocarcinomas and therefore were of no use in distinguishing between these 2 entities. CONCLUSION: A panel of monoclonal antibodies against cytokeratins 7 and 20 antigens, CA125, and carcinoembryonic antigen is useful in differentiating serous and endometrioid adenocarcinomas of the ovary from colonic adenocarcinomas. Mucinous ovarian adenocarcinomas cannot be distinguished from colonic adenocarcinomas using immunohistochemistry.