The HCS Mitochondrial Health Kit simultaneously and quantitatively measures two important cell-health parameters: mitotoxicity and cytotoxicity. The MitoHealth stain detects changes in the mitochondrial membrane potential, whereupon the reagent accumulates in active mitochondria. The kit includes the Image-iT® DEAD™ Green to detect cytotoxicity, an impermeant dye to healthy cells that becomes permeant when the plasma membrane of cells is compromised. Both indicators are amenable to fixation and permeabilization, thus allowing for multiplexing with other biomarkers of interest. The blue-fluorescent nuclear segmentation tool Hoechst 33342 is also included and stains DNA in both live and dead cells.