The Guava ViaCount® Flex Reagents were developed to expand the number of cell types that can be stained and counted with the ViaCount assay. The original Guava ViaCount Reagent is formulated for rapid and easy viability assessment and counting of mammalian cells. The Guava ViaCount Flex Reagents were formulated to enable accurate counting and discrimination of viable and nonviable cells for a variety of difficult cell samples.