Thiazolyl blue tetrazolium bromide also called MTT is a cell-permeable and positively charged tetrazolium dye commonly used as a sensitive and reliable method to assess cell viability, proliferation, cytotoxicity, and apoptosis. Nicotinamide adenine dinucleotide phosphate (NADPH)-dependent cellular oxidoreductase of living cells reduces the MTT to its insoluble, dark blue MTT-formazan which can be colorimetrically measured at a wavelength of 570 nm (500-600 nm). The MTT assay is a sensitive and reliable colorimetric assay for measuring cell metabolic activity and has been widely used to assess cell viability. However, as the enzymatic reduction of 3-[4,5-dimethylthiazole-2-yl]-2,5-diphenyltetrazolium bromide (MTT) to MTT-formazan is catalyzed by mitochondrial succinate dehydrogenase, the MTT assay is dependent on mitochondrial respiration and indirectly serves to assess the cellular energy capacity of a cell.