Resazurin (7-hydroxy-10-oxidophenoxazin-10-ium-3-one, sodium) is a blue fluorogenic dye used as a redox indicator in cell viability and proliferation assays for bacteria, yeast or mammalian cells. The blue form of the dye is irreversibly reduced by enzymes in viable cells to generate a highly red-fluorescent product, resorufin, which exhibits an emission maximum at ~595 nm and can be detected by flow cytometry, fluorescence microscopy, and high-throughput screening methods. Resazurin is minimally toxic to living cells, making it suitable for use in long-term cell culture. The dye has also been used to assay L-glutamate and to measure the metabolic activity of mitochondria.