A radioimmunoconjugate comprised of a chimeric monoclonal antibody against human carcinoembryonic antigen (CEA) conjugated with the radioisotope yttrium 90 (Y-90) via the chelator tetra-azacyclododecanetetra-acetic acid (DOTA) with potential antineoplastic activity. The antibody moiety of yttrium Y90 DOTA anti-CEA monoclonal antibody cT84.66 binds to cells expressing the CEA antigen. Upon cellular internalization, this agent selectively delivers a cytotoxic dose of beta radiation. CEA, a tumor associated antigen, is overexpressed in many cancer types, including gastrointestinal, breast, non-small cell lung, and thyroid cancers.