A radioimmunoconjugate consisting of the humanized CH2 domain-deleted monoclonal antibody CC49 and iodine I 131 with antineoplastic activity. Monoclonal antibody CC49-deltaCH2 targets the tumor-associated glycoprotein 72 (TAG-72) that is expressed by a wide range of human neoplasms including colorectal, gastric, pancreatic, ovarian, endometrial, breast, non-small cell lung, and prostate cancers. Iodine I 131 monoclonal antibody CC49-deltaCH2 binds to tumor cells expressing TAG-72, selectively delivering a cytotoxic dose of beta and gamma radiation.