We describe a rapid and reliable method to quantitate the extent of apoptosis in neuronal cell cultures. Based on their annexin V-affinity, resulting from phosphatidylserine (PS) exposure at the outer leaflet of the plasma membrane, apoptotic cells can be distinguished from annexin V-negative living cells, by using microscopic and flow cytometric procedures. When combined with propidium iodide (PI) the double labeling procedure allows a further distinction of necrotic (annexin V+/PI+), apoptotic (annexin V+/PI-) cells. Furthermore, when the cells are incubated with annexin V prior to harvesting, the former cell populations can be separated from cells damaged during isolation (annexin V-/PI+). In the present paper, we show that the annexin V-binding assay is also applicable to differentiated neuronal cells with fragile neurite outgrowths.