Cell viability assays are used in order to measure the physical and physiological health of cells in response to extracellular stimuli, or chemical agents. Most cell viability assays can be utilized in fluorescence microscopy, microplate readers, and flow cytometry. Commonly used assays include MTT assay, trypan blue exclusion assay, and PI staining assay. Each assay has a specialized reagent that determines viability based on cellular membrane integrity, metabolic activity, and enzymatic activity. After the incubation period, single or multi-parameter assays are used to detect multiple measures of cell death. These assays allow for the simultaneous detection of viable, dead, and dying cells. Cells are analyzed by measuring fluorescence, absorbance, luminescence, or other signals associated with cell viability.