The use of monoclonal antibodies (MAbs) in the clinical management of carcinoma patients is reported in the present review. Among the various MAbs generated, MAb B72.3 (LTIB, National Cancer Institute, U.S.A.) has been extensively used in clinical trials either for antigen identification (TAG-72) in sera, or for tumor localization in carcinoma patients. Serum assay results, in colorectal cancer patients, showed the usefulness of the MAb B72.3 in monitoring the clinical course of the malignant disease. Its specific tumor localization (70% of the biopsy specimens) and the immunoscintigraphy studies, after in vivo administration, have also been discussed. The positive results obtained, markedly contributed in the development of a new intraoperative methodology termed "radioimmunoguided surgery".