FDA/PI Stain is a combination of fluorescent dyes for assessing the viability of diverse cell types including mammalian cells, yeast, and pollen grains. FDA is a non-fluorescent dye that permeates cell membranes, undergoing hydrolysis by the esterase activity of viable cells and producing the green fluorescent compound fluorescein. FDA can be retained in viable cells with intact membranes, acting as a live cell marker. PI, a red membrane-impermeable dye, selectively penetrates dead or damaged cells with compromised membranes. PI is a commonly used dead cell marker binding to DNA and RNA through intercalation. Upon binding, a fluorescence intensity of PI can be increased by 20- to 30- fold higher.