A radioimmunoconjugate of the humanized monoclonal antibody CC49 labeled with iodine I 131. Iodine I 131 monoclonal antibody CC49 delivers beta and gamma radiation-emitting I 131 radionuclide specifically to tumor cells that express tumor-associated glycoprotein (TAG)-72, allowing localization of TAG-72-expressing tumor cells with radioimaging devices in diagnostic applications or resulting in specific TAG-72-expressing tumor cell radiocytotoxicity in therapeutic applications. Monoclonal antibody CC49 binds to TAG-72, a pancarcinoma antigen, with high affinity.