Monoclonal antibodies have become widely investigated in the Nuclear Oncology, especially in the radioimmunosassay of tumor markers and in vivo radioimmunoimaging of cancer. However, there are numerous factors as to whether radioimmunoimaging will ultimately successful. For imaging of tumors, metallic radionuclides such as In-111, Ga-67, Tc-99m have favorable nuclear properties than widely used I-131. These radioistopes have characteristics of the useful radiation for imaging, convenient short half-lives and the simple and rapid radiolabeling of monoclonal antibodies by using bifunctional chelaing agents. The obtained chelate-tagged antibodies are quite stable both in vitro and in vivo, without interfering antibody activities and animal experiments provided a good basis for its clinical applicability for the radioimmunoimaging of cancer. Much attention has also been given to the possibility, only beginning to be exploited, of the specific treatment of malignant neoplasms with these agents. Although specific antibody has not been developed that is uniquely specific for cancer alone and there are still many questions to be answered and problems to be overcome before radioimmunoimaging can be successfully used in ptients with cancer, these methods can be applied to the coupling of monoclonal antibodies with anti-neoplastic drugs or radionuclides suitable for internal radiation therapy of cancer.