Phosphatidylserine (PS) is translocated from the inner to the outer surface of the cell for phagocytic cell recognition. The human anticoagulant, Annexin V, is a 35 kDa Ca2 -dependent phospholipid protein with a high affinity for PS. Annexin V labeled with CF®488A (Abs/Em= 490/515 nm) can identify apoptotic cells in green by binding to PS exposed on the outer leaflet. Our CF®488A dye is superior to fluorescein/FITC as it is not affected by pH and has much better photostability. Propidium iodide (PI) is impermeant to live cells or early apoptotic cells, but stains necrotic cells and late apoptotic cells with red fluorescence (Abs/Em with DNA = 535/617 nm) . Both PI and Annexin V-CF®488A can be excited using the 488nm line of a flow cytometer.