Diabetic patients are more prone to infection and evidence for an immunologic defect superimposed upon the metabolic abnormalities of diabetes is convincing. Neutrophils play a critical role in the host defense mechanism against various bacterial infections, and it is suggested that impaired neutrophil functions cause susceptibility to infections in diabetic patients. To explore the possibility that Granulocyte colony-stimulating factor (G-CSF) may be useful to prevent the morbidity and mortality caused by infections in diabetics. We studied the effect of G-CSF against septicemia in diabetic rats. Forty eight rats were divided into seven equal groups. The IInd, IVth-VIth groups were made diabetic by single intraperitoneal injection of streptozotocin. Fourth, VIth and VIIth groups were made septicemic by cecal ligation and perforation at the end of the second week of streptozotocin injection. G-CSF was subcutaneously injected into IIIrd, Vth and VIth groups. White blood cell count, neutrophil counts and function were determined. Rats in all groups were also observed for seven days for survival. White blood cells, neutrophil and lymphocyte counts and the neutrophil phagocytosis index decreased but neutrophil adherence rate was not different in diabetic group II (p<0.05). All these variables were significantly diminished in diabetes and sepsis-induced group IV (p<0.05). G-CSF injections improved all variables except neutrophil adherence. Cumulative survival ratio was better in G-CSF-injected group VI than in ceftriaxon-administrated group VII (p<0.05). In conclusion, G-CSF increased neutrophil counts, developed neutrophil functions and improved survival. These results suggest that G-CSF may be useful as a drug to prevent bacterial infection in diabetic patients.