Abstract: A method of analyzing and separating the three major populations, namely, lymphocytes, monocytes and granulocytes of white blood cells from a composite histogram containing the various types of white blood cells is provided by identifying a mode (highest frequency of occurrence) of both the lymphocyte and granulocyte concentrations by determining the highest sum of such populations over first predetermined ranges in the histogram. This is accomplished by determining the lymph and gran peaks along with 60% thresholds from said peaks and estimating the lymph and gran areas in providing a reconstituted lymph and gran curve. Lymph and gran population curves are then subtracted from the histogram resulting in a mid population curve whose peak is determined and from which is derived left and right thresholds based on the mid population peak.