Repeated injections or infusion of hematopoietic growth factors, such as interleukin-3 (IL-3), granulocyte macrophage-colony stimulating factor (GM-CSF), or granulocyte-colony stimulating factor (G-CSF), accelerate restoration of hematopoiesis in animals compromised by sublethal doses of cytotoxic drugs or irradiation. Previous work by the investigators has shown that IL-1 induced circulating CSF in normal mice and, when used after sublethal irradiation, accelerated the recovery of endogenous splenic colonies. Therefore, IL-1, as well as IFN-gamma, tumor necrosis factor (TNF), G-CSF, and GM-CSF, were evaluated as potential therapeutic agents in irradiated C3H-HeN mice. A single intraperitoneal injection, administered within three hours after a lethal dose (LD)95/30 of irradiation that would kill 95% of mice within 30 days, protected in a dose-dependent manner up to 100% of mice from radiation-induced death due to hematopoietic syndrome. Significant therapeutic effects were also achieved with a single dose of IFN-gamma or of TNF. In contrast, GM-CSF and G-CSF, administered shortly after irradiation, had no effect in the doses used on mice survival.