MTT or (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and resazurin assays are both used to measure cellular metabolic activity and monitor cell proliferation, viability, and cytotoxity. MTT is a colorimetric based assay. Because it is an insoluble product, the cells need to be lysed to make the formazan salt more soluble before absorbance can be measured. Resazurin can be measured using either colorimetric or fluorescence detection. It does not require cell lysis, allowing kinetic monitoring of the same samples at different points in time.