Mitochondrial membrane potential, (ΔψM), is an important parameter of mitochondrial function used as an indicator of cell health. JC-1 is a lipophilic, cationic dye that can selectively enter into mitochondria and reversibly change color from green to red as the membrane potential increases. In healthy cells with high mitochondrial (ΔψM), JC-1 spontaneously forms complexes known as J-aggregates with intense red fluorescence. On the other hand, in apoptotic or unhealthy cells with low (ΔψM), JC-1 remains in the monomeric form, which shows only green fluorescence. Cayman's JC-1 Mitochondrial Membrane Potential Assay Kit provides all the necessary reagents, as well as complete instructions, for analysis of mitochondrial integrity in whole cells. The assay is applicable to fluorescence microscopy and fluorescent plate reader. For flow cytometry, Cayman's JC-1 Mitochondrial Membrane Potential Flow Cytometry Assay Kit (Item No. 701560) is recommended.