Abstract: Leukopenia model were induced by intraperitoneal injection of cyclophosphamide （100,150，200 and 250mg/kg） in KM mice. The peripheral WBC of the mice were decreased dramatically and to the lowest level 4 days after the injection, thereafter began to rise and exceed the pre-injection level at 6th day and then remained for a long period. The lowest level of WBC is linear-negatively correlative with the cyclophosphamide dosage.According to the complete inactivation of cyclophosphamide in the body after 4 hours and the dynamic changes of WBC,the dynamic process and chronaxia of WBC growth were analysed.The results suggested that any chemotherapy resulting in the change of peripheral WBC chronaxia of the model mouse may be considered having the effects on leukopenia.

Key words: Cyclophosphamide, Mice, WBC, Dynamics, Leukopenia