32P is effective therapy for polycythemia and primary thrombocytosis. The Polycythemia Vera Study Group is comparing radioactive phosphorus with alkylating agents to determine relative efficacy. Less well investigated is the effectiveness of 32P vs. busulfan in chronic granulocytic leukemia. Endolymphatic administration of radiopharmaceuticals may play a role in the therapy of infradiaphragmatic lymphoma. Among the radionuclides that have at times been used in hematology are 32P, 198Au 24Na, 76As, 89Sr, 52Mb, 54Mn, 91Y, 95Zr, 95Cb, 111Ag, 109Pd, 131I, 185W, and 192Ir. As stated, 32P has proven single most efficacious agent. The hematologic diseases that have been treated include both malignant and benign conditions. Among the malignant conditions are polycythemia vera, agnogenic myeloid metaplasia, thrombocythemia, leukemia, Hodgkin's disease, and multiple myeloma. Hemophilia, and Osler--Weber--Rendu disease are among the benign entities in which the agents have been tried. Polycythemia and thrombocythemia remain those in which the greatest success has been achieved.