Thiazolyl Blue Tetrazolium Blue (MTT) may be used in measurement of cell proliferation.. MTT produces a yellowish solution that is converted to dark blue, water-insoluble MTT formazan by mitochondrial dehydrogenases of living cells. The blue crystals are solubilized with acidified isopropanol and the intensity is measured colorimetrically at 570 nm. MTT has been used as a histochemical/cytochemical reagent and for the detection of NAD. ADP-linked enzyme systems in tissue cannot be detected with MTT, due to binding of the cation by the cyanide trap used. MTT is rapidly reduced to the formazan, which chelates with nickel, copper, and cobalt; the cobalt chelate has been used in oxidative systems.