<p>A method of classifying and counting leucocytes with abnormal DNA content which comprises: (1) the step of treating a hematological sample with a hemolytic agent and staining cells in the thus hemolyzed sample with a fluorescent dye capable of showing a difference in fluorescent intensities of at least matured leucocytes, leucocytes with abnormal DNA content and immature leucocytes; (2) the step of introducing the sample containing the stained cells into a flow cytometer and measuring the scattering light and the fluorescence of each cell; (3) the step of separating leucocytes from aggregated platelets and simultaneously passing cells with the use of a difference in scattering light peaks and a difference in scattering light widths ; and (4) classifying the leucocytes separated in the step (3) into mature leucocytes, leucocytes with abnormal DNA content and immature leucocytes with the use of a difference in scattering light intensities and a difference in fluorescent intensities of the cells followed by counting.</p>
