viability measurement method Compound cytotoxicity is an important parameter to measure when developing potential human therapeutics. Cytotoxicity is determined as a measure of radioisotope (3H thymidine or 51Cr) release, lactate dehydrogenase release from damaged cells, tetrazolium salt and alamar blue reduction, fluorescent dyes that selectively stain live or dead cells, and decrease in ATP content. The viability reporter technologies measure cell life or death by quantitating ATP content, caspase activity, membrane potential, and so on. assay design method