MTT Method: MTT is a colorimetric assay and this method is far superior to the previously mentioned methods as it is easy-to-use, safe, has a high reproducibility, and is widely used in both cell viability and cytotoxicity tests. The MTT assay is the best known method for determining mitochondrial dehydrogenase activities in the living cells. In the method, MTT is reduced to a purple formazan by NADH. MTT forms purple needle shaped crystals in the cells therefore prior to measuring the absorbance, an organic solvent is required to solubilize the crystals.