Abstract: BACKGROUND ＆ ATM: To establish an automatic scoring method based on a single_laser flow cytometer for detection of frequencies of micronucleated polychromatic erythrocytes from rat marrow. MATERIAL AND METHODS:Male Wistar rats were exposed to cyclophosphamide (CP) and their frequencies of micronucleated polychromatic erythrocytes (FMNPCE) as well as frequencies of micronucleated normochromatic erythrocytes (FMNNCE) were detected by manual scoring and a single_laser flow cytometer based on AO staining. RESULTS:Using Forward angle scatter(FSC) and DNA fluorescence(FL1)to protract contour configuration histograms,they showed five distinct cell populations which were total nucleated cells,polychromatic erythrocytes,normochromatic erythrocytes,micronucleated polychromatic erythrocytes and micronucleated normochromatic erythrocytes respectively；both manual and flow cytometric methods demonstrated positive dose_response trends and time_related increase for fMNPCE and fMNNCE in rat bone marrow; comparison of the results by the two methods showed good correlation between them and curve fit analysis showed the equation was =1.0967＋1.0639X(R=0.949，P<0.01). CONCLUSION: An automated scoring method based on a single_laser flow cytometer for detection of frequencies of frequencies of micronucleated polychromatic erythrocytes from rat marrow is established.

Key words: micronucleus test, flow cytometry, automatic measurement, rats