In the MTT assay, cells are incubated with the MTT reagent. Metabolically active cells reduce the MTT reagent to formazan, which accumulates as [insoluble crystals](). These crystals can be dissolved using a solubilizing agent like DMSO (dimethyl sulfoxide), and the resulting solution can be quantified by measuring its absorbance using a spectrophotometer at a wavelength of 570 nm. The amount of formazan produced is directly proportional to the number of living cells.
