Human leukemia has been determined and classified with the help of flow cytometry for the past two decades. Past attempts to detect leukemia blasts relied on both forward and side scatter (FSC and SSC) based on cell size and granularity. However, this technique failed to show a clean separation of blasts from normal lineage cells. In 1993, Borowitz, et al developed flow cytometric analysis to distinguish human leukemia blasts from other normal lineage cells by using fluorescence-conjugated CD45 antibodies (1). On CD45-SSC plots, the blasts are distinctly located below granuocytes in human acute myeloid leukemia. This technical advance has significantly improved diagnosis and classification of human leukemia.