instaCELL cytotoxicity assay kits have been designed to improve the reliability and reproducibility in routine toxicity testing. The assay kit includes aliquots of cryopreserved assay ready cells which have been optimized and validated for the particular purpose. The cells can be used like a reagent instantly after thawing and don’t need to be cultivated or even counted before. The kit further includes assay plates, recovery buffer, assay medium, proper controls, and a viability testing reagent (Resazurin or MTT). All components are carefully adjusted to the assay ready cells included in the kit, to provide comparable result, wherever or whenever the kit is used by whoever. In a regulated testing environment e.g. for the evaluation of medical devices (ISO 10993‐5 399‐5) or the estimate of in vivo starting doses (ICCVAM guidance documents), the use of the validated kits eliminates a major factor of bioassay variability, the cultivation and quality of the cells.