At 1000 Rads of acute total body exposure, the bone marrow is irreversibly damaged. Lymphocytes, neutrophils and platelets all become absent by 5, 10 and 15 days respectively. Circulating red cells are not appreciably affeced due to their relatively long life. The patient will invariably die of either infection or bleeding if there is no aggressive therapy. Bone marrow transplant is an option. Protective isolation is imperative. Even with these forms of aggressive treatment, the prognosis is poor.