Targeted antibody therapy represents a promising approach for the treatment of cancer. However, antibodies that bind to cancer cells are often, by themselves, not cytotoxic. Recombinant immunotoxins (RITs) are chimeric proteins composed of the variable fragment (Fv) of a monoclonal antibody fused to a portion of a powerful bacterial toxin. The Fv replaces the cell-binding domain of the toxin and directs the toxin to cancer cells that express an internalizing target antigen. RITs are very potent and are able to kill cells that are resistant to standard chemotherapy. Results from clinical trials indicate that RITs that are designed to combine antibody selectivity with toxin cell-killing potency will be useful additions to cancer therapy.