depleted during the latent period until their viability falls below the levels required for homeostasis. The appearance ofsigns and symptoms of incompetence in one or more systems marks the onset of the manifestillness (Phase III). These dose-related syndromes are (1) hematopoietic, with signs and symptoms of increasing leukopenia reaching a nadir 28-30 days after an acute sublethal dose; (2) gastrointestinal, with radiogenic injury to the gastrointestinal tract resulting in vomiting, bloody diarrhea, fluid and electrolyte shifts, malabsorption and (3) cerebro- or cardiovascular (formerly known as the central nervous system syndrome), with early and increasingly severe signs and symptoms ofincreasing intracranial pressure due to cerebral edema associated with a generalized vasculitis. In the absence of treatment, death (Phase IV) can occur 48 hours to 60 days after acute exposure to doses in the lethal range (LD ~3.25 Gy to bone marrow). The LDsg may be increased to 8-9 Gy with modern treatment modalities. The exposure-to-death interval decreases with increasing dose. Spontaneous recovery (Phase IV) maybe anticipated after day 30 amongindividuals exposed to radiation at sub-lethal levels (27). 3.2.2.2 Acute Local Radiation Injury Except for doses in the range of several hundreds of grays, acute local irradiation alone is unlikely to cause a significant whole-body effectorcritical illness in the immediate postexposure period. Local radiation injury can result from exposure to a source of penetrating radiation, close proximity to or contact with a f radiation source, or contamination with B emitting radionuclides. The earliest observable effect of local exposure above threshold levels (~6 Gy)is a transient erythema that appears within two to three hours. It possibly is associated with the release of endotoxins from necrotic cells. Except for this reaction, the effects of doses of less than several hundreds of grays to skin do not become apparent for several days or longer, depending on the dose. One or more waves of erythemawill follow approximately five or more days after moderate local doses (~20 Gy). These waves are associated with radiation damage to endothelial cells and initially reflect capillary incompetence. With increasing dose, subsequent waves of erythema and increasing edemareflect expression of radiation damage affecting larger and deeper vessels. The deeper damage can affect other