Monoclonal antibodies against a tumor-associated antigen (TAG-72) with mucin-like properties have been generated. MAb B72.3 was used to identify and help characterize this antigen. B72.3 has been successfully used for the localization of tumor metastases in situ after i.v. administration. MAb B72.3 has also been used in conjunction with CC49, another anti-TAG-72 MAb, to measure TAG-72 levels in sera and effusions. TAG-72 can be found in the fluids of patients with adenocarcinomas from many different sites. This CA 72-4 double determinant radioimmunoassay in conjunction with assays for carcinoembryonic antigen can identify patients with malignancies with greater sensitivity than either assay alone.