Adenosine 5'-triphosphate (ATP) is the chemical energy for cellular metabolism and is often referred to as energy currency of the cell. ATP is produced only in living cells during photosynthesis and cellular respiration and consumed in cellular processes including biosynthetic reactions, motility and cell division. It is a key indicator of cellular activity and has been utilized as a measure of cell viability and cytotoxicity in research and drug discovery. This Cytotoxicity Assay Kit provides a rapid Method to measure intracellular ATP, cell viability and cytotoxicity. The single working reagent lyses cells to release ATP, which, in the presence of luciferase, immediately reacts with the Substrate D-luciferin to produce light. The light intensity is a direct measure of intracellular ATP concentration and hence number of living cells. This non-radioactive, homogeneous cell-based assay can be conveniently performed in microplates. The reagent is compatible with all culture media and liquid handling systems for high-throughput screening applications in 96-well and 384-well plates.