Five hundred Rads of acute total body exposure falls near the LD 50/60. The hematologic responses become even more profound. The lymphocyte response is seen first with a decrease to 20% of the normal level occurring within the first several days. The curious neutrophil response is once again seen as in the 200 R exposure, but to a more exaggerated degree. Symptoms of increased susceptibility to bleeding and infection occur at approximately 3 weeks post exposure. All three curves reach their lowest at about 4 weeks post exposure. If the patient survives this phase, the hematologic recovery is complete at 6 months.