Granulocyte colony stimulating factor (G-CSF) stimulates the proliferation of progenitor cells committed to myeloid differentiation. In animal models, G-CSF is able to stimulate granulocyte recovery and promote survival after lethal or sublethal irradiation when administered as daily injections, suggesting an influence on the residual hematopoietic primitive precursors surviving irradiation. In this study, we clearly demonstrate that a single dose of G-CSF (1 mg/kg) administered to B6D2F1 mice 2 hours after a lethal dose 95/30 irradiation achieves a 78% survival at day +30 after irradiation. Survival of G-CSF treated mice compares favourably with that of syngenic bone marrow transplantation recipients (78% vs 90%, ns).