Quantification of number of viable cells is an indispensible tool in Cell Biology research. BioVision’s Calcein AM Cell Viability Assay Kit is a fluorometric method for extremely sensitive quantification of viable cells that can detect as low as 50 viable cells in less than 30 min. Calcein AM is a non-fluorescent, hydrophobic compound that easily penetrates intact and live cells. Hydrolysis of Calcein AM by intracellular esterase produces a hydrophilic, strongly fluorescent compound that is retained in the cell cytoplasm and can be measured at Ex/Em = 485/530 nm. The measured fluorescence intensity is proportional to the number of viable cells. This assay kit provides an easy-to-use, non-radioactive, and high-throughput method for cell proliferation, cell viability, chemotaxis, cytotoxicity and apoptosis.