A tri-Fab bispecific monoclonal antibody (BiMoAb) divalent for the carcinoembryonic antigen (CEA) and monovalent for histamine-succinyl-glycine (HSG) peptide-hapten radiolabeled with iodine I 131 (I131) with antigen-binding and radioisotopic activities. Iodine I 131-labeled anti-CEA/anti-HSG bispecific monoclonal antibody TF2 binds to the tumor-associated antigen (TAA) CEA on CEA-expressing tumor cells; these cells may then be radioimaged scintigraphically.