CJ-50001 is a recombinant granulocyte-colony stimulating factor (rG-CSF) developed by Cheil Jedang R&D Center. The effects of CJ-50001 on the increase of peripheral neutrophil count following intravenous and subcutaneous single administration at a dose of 20$mu$g/kg in normal ICR mice and SD rats, respectively, were compared with those of Grasin, a control drug. Both CJ-50001 and Grasin significantly increased the peripheral neutrophil number in four treatment groups and the maximum number of neutrophil was achieved at 12 to 18 h in rats and mice, respectively. The dose dependency test was studied for CJ-50001 only in normal mice by intravenous or subcutaneous administration. When administered i.v or s.c at the various doses in normal mice, CJ-50001 significantly increased the neutrophil number over the dose of 160 ng/kg, compared with the vehicle control group. From these results, it was concluded that CJ-50001 showed efficacy similar to Grasin in the peripheral neutrophil count increase.