Alpha particles are short-ranged high-energy radiations capable of killing in a range of 1 to 3 cells. We are attempting to deliver alpha-emitting isotopes to leukemia cells and small solid tumors using antibodies as ligands. Bi-213 and Ac-225 are purified and chelated to the Ig. Biochemistry of the agents, radiobiology, and pharmacology are studied. Model systems under study include myeloid leukemias, prostate cancer, and lymphoma. Human trials are initiated once clinical scale-up is accomplished.