Abstract: Purpose : Studies were conducted to evaluated the effect s of one t reatment protocol and sampling time on the micronucleus test s of two clastogens - mitomytin C and cyclophosphamide. Methods : Young adult ICR mice were t reated once with mitomytin C (MMC , 2 mg/ kg. bw) or cyclophosphamide (CP , 40 mg/ kg. bw) by int raperitoneal injection. The micronucleus incidences in polychromatic erythrocytes ( PCEs) of different sampling times - 12 h , 18 h , 24 h ,32 h , 48 h , 72 h after dose were evaluated in the peripheral blood and the bine marrow. Results : The date in this study indicated : ①The f requencies of micronucleatde polychromatic erythrocytes (MnPCEs) in the bone marrow and peripheral blood were almost identical at each optimal sampling time of the two clastogens ; ② The maximal increase of the incidence of MnPCEs of peripheral blood was delayed 12～14 h compared to that of bone marrow ; ③ The f requency of PCEs of peripheral blood was equal sensitive to that of bone marrow in detecting cytotoxicity to the h ematopoitic system. Conclusion : It is suggested that followingthe one injection protocol with MMC or CP , bone marrow and peripheral blood are both equaly efficacy.

Key words: micronucleus test (assay), polychromatic erythrocyte (PCE), bone marrow, peripheral blood