This product detects apoptotic cells with changes in nuclear chromatin condensation and plasma membrane permeability, using three nucleic acid stains: UV-excitable Hoechst 33342, green fluorescent YO-PRO™ dye, and propidium iodide. The YO-PRO™ dye can enter apoptotic cells, whereas red-fluorescent propidium iodide (PI) cannot. Thus after staining with YO-PRO™-1 dye and PI, apoptotic cells show green fluorescence, and dead cells show primarily red fluorescence and some green fluorescence. Blue fluorescent Hoechst 33342 brightly stains the condensed chromatin of apoptotic cells and more dimly stains the normal chromatin of live cells. The staining pattern resulting from the simultaneous use of these three dyes makes it possible to distinguish normal, apoptotic and dead cell populations by flow cytometry or fluorescence microscopy.