The LIVE/DEAD® Fixable Dead Cell Stain Kit employs an amine-reactive fluorescent dye to evaluate mammalian cell viability by flow cytometry. In cells with compromised membranes, the dye reacts with free amines both in the cell interior and on the cell surface, yielding intense fluorescent staining. In viable cells, the dye's reactivity is restricted to the cell-surface amines, resulting in less intense fluorescence. The difference in intensity between the live and dead cell populations is typically greater than 50 fold, and this fluorescence intensity discrimination is completely preserved following formaldehyde fixation. These single-color assays use only one channel of a flow cytometer, making the reactive dyes in the LIVE/DEAD® Fixable Dead Cell Stain Kits compatible with multiparameter staining experiments. The red-fluorescent reactive dye (L23102) has excitation and emission maxima of ~595/615 nm. Also available are LIVE/DEAD® Fixable Dead Cell Stain Kits that contain blue-fluorescent reactive dye (L23105), violet-fluorescent reactive dye (L34955), and green-fluorescent reactive dye (L23101).