Boron neutron capture therapy, a binary form of cancer treatment, has the potential to deliver potent cytotoxic radiation to tumor cells with minimal collateral damage to normal tissues if methods for the selective accretion of elevated concentrations of boron-10 in tumor can be developed. In this regard, a monoclonal antibody with dual specificity, for both anionic boron cluster compounds (nido-carboranes) and a tumor-associated antigen (carcinoembryonic antigen, CEA), was produced. The specific binding of a nido-carborane to CEA-expressing tumor cells was achieved using this bispecific antibody. The ability of this bispecific antibody to concentrate selectively at tumor sites in vivo has also been demonstrated, thus suggesting its potential for sequestering boron-rich compounds in tumors.