BV421 is a polymer-based dye excited by the violet laser and is one of the brightest fluorochromes offered by BD Biosciences. Conjugates are typically 10 times brighter than Pacific Blue™ conjugates and are often as bright as or brighter than PE conjugates. Due to nearly identical excitation and emission properties but different spillover characteristics, BD Horizon BV421, Pacific Blue™, and BD Horizon™ V450 cannot be used simultaneously.