Annexin V has a high affinity for phosphatidylserine (PS), which becomes exposed on the outer leaflet of cells undergoing apoptosis. Because of this affinity, fluorescently labeled annexin V reagents are commonly used in apoptosis research. The annexin V, Pacific Blue™ conjugate is violet excitable, making it ideal for instruments with a violet laser and for multicolor experiments that include green- or red-fluorescent dyes.