Abstract: BACKGROUND ＆ AIM: To evaluate the effects of different doses of cyclophosphamide (CP) and sampling time on mouse micronucleus frequency in bone marrow. MATERIAL AND METHODS: Young adult NIH mice were treated with a sigle dose of CP(40 or 80 mg/kg) by intraperitoneal injection. The micronucleus freqyuency in bone marrow polychromatic erythrocytes (PCE) at different sampling time 18 , 24 , 48 h after treatment was evaluated. RESULTS: Our data showed: ① The changing trends of the micronucleus frequencies in PCE in the two groups receiving 40 mg/kg and 80 mg/kg of CP were the same at different sampling times. The peak time of the micronucleus incidence was at 24 h after treatment. ② The ratios of PCE to NCE of the two treated groups were not significantly different from the control group. This indicated that the mice bone marrow cells were not suppressed by one CP of 40 or 80 mg/kg by intraperitoneal injection. ③ The micronucleus frequency in PCE of 40 mg/kg was significantly different from that of 80 mg/kg, showing a dose_response relationship. CONCLUSION: CP can be used as a positive control of micronucleus test. The dose range of 40～80 mg/kg was fine, and the optimal sampling time is at 24 h after treatment.

Key words: micronucleus frequency, cyclophosphamide, polychromatic erythrocyte, bone marrow