In Flow Cytometry, the term lysis is related to the process of lysing non-nucleated blood cells (i.e. red blood cells) in order to avoid any interference with the immunophenotyping of nucleated blood cells. The basic disadvantage of most protocols is the uncontrolled lysis of nucleated blood cells. Even widely accepted reagents, like ammonium chloride, bear high risk of uncontrolled leukocyte losses or cell damage, especially in pathological samples. With the CyLyse® kit, Partec offers wash and no-wash erythrocyte lysing reagents with or without fixation, therefore reducing undesired lysis of nucleated blood cells close to zero. In combination with absolute volumetric counting, this lysing reagent guarantees accurate white blood cell counts even on problematic patient samples. It has been demonstrated in extensive studies that this reagent is particularly suitable for delicate assays such as the determination of CD34+ cells and cell counting of rare events. CyLyse® is recommended as a general lysing reagent for absolute cell counting and assays where minimum loss of nucleated blood cells is essential.