Resazurin (7-hydroxy-10-oxidophenoxazin-10-ium-3-one, sodium) is a blue non-fluorescent dye used as a cell viability and proliferation indicator for bacteria, yeast and mammalian cells. Dehydrogenase enzymes in the mitochondrial respiratory chain of the metabolically viable cells irreversibly reduce the oxidized form (blue) of the dye to resorufin (a highly pink-fluorescent product), which exhibits an emission around 590 nm. Resazurin was originally used to test bacterial and yeast contamination in milk and other biological fluids. The Resazurin Cell Viability assay is a fluorescent/colorimetric assay that measures cellular metabolic activity based on conversion of the resazurin reagent to resorufin. As the conversion only occurs in metabolically active cells, the amount of The fluorescent or colorimetric signal generated due to resorufin production is proportional to the number of viable cells in the sample. The reduction of resazurin to resorufin in the assay can be quantified either by measuring the fluorescent intensity at 590 nm (590-620 nm) with the excitation at 550 nm (530-570 nm), or the optical density at 570 nm. To measure cell viability using an alternative method use our XTT Colorimetric Assay Kit (Cat. No. ZX-44117), LDH‐Cell Cytotoxicity Assay Kit (Cat. No. ZX-44118), or Sulforhodamine B (SRB) Cell Cytotoxicity Assay Kit (Cat. No. ZX-44119).