The ToxiLight BioAssay Kit is a bioluminescent, non-destructive cytolysis assay kit designed to measure the release of the enzyme, adenylate kinase (AK), from damaged cells. AK is a robust protein present in all eukaryotic cells, which is released into the culture medium when cells die. The enzyme actively phosphorylates ADP to form ATP and the resultant ATP is then measured using the bioluminescent firefly luciferase reaction. As the level of cytolysis increases, the amount of AK in the supernatant also increases, which results in emission of higher light intensity by the ToxiLight reagent. Because the ToxiLight BioAssay Kit exploits the fact that AK is released from cells when they die, there is no need for cell lysis (unlike many other cytotoxicity assays). Repeated samples of supernatant can therefore be taken over time without disrupting the cells themselves. This allows for kinetic analysis of cell death.