Abstract: A lytic reagent composition and the method of use for differential analysis of leukocytes using flow cytometry are disclosed. The lytic reagent composition includes a short chain alkyl oxyethanol, such as 2-methoxyethanol, 2-ethoxyethanol, 2-propoxyethanol, or 2-isopropoxyethanol, in a sufficient amount to preserve leukocytes; a non-lysing nonionic surfactant as a debris solublizer; and an inorganic buffer to maintain pH of the lytic reagent composition in a range from 9.1 to 10.7. The lytic reagent composition is used to lyse red blood cells and preserve leukocytes, as well as used as the sheath reagent for the focus flow measurement. The lytic reagent composition, when used on a flow cytometric analyzer with multiple angle light scatter and light absorbance measurements, enables differentiation of leukocytes into five subpopulations.