Abstract: Effective antibody therapy of cancer depends on the selective delivery of a highly potent cytotoxic effector to the tumor cells. While antibodies specific for lineage or differentiation antigens can provide selective delivery, they are often not potent. Alpha particle emitters and nano-scale generators of alpha particle emitting elements can be delivered to the inside of tumor cells by the use of antibodies to internalizing protein targets. Such constructs have now shown clinical activity and tolerability in human Phase I and Phase II trials. Improved potency may be achieved by use of alpha emitters carried by single wall carbon nanotubes that allow increased payloads while at the same time rapid renal clearance to avoid toxicity. The use of antibodies to truly tumor specific antigens found in the inside of cells is now possible to further increase tumor specificity.