The enzyme lactate dehydrogenase (LDH) is a cytosolic enzyme present in the cells and can be used as an indicator of cytotoxicity. Our LDH-Cytotoxicity Assay Kit is a non-radioactive colorimetric assay, which quantitatively measures the lactate dehydrogenase (LDH), a cytosolic enzyme that is released upon cellular damage. The released LDH is measured, using a coupled enzymatic reaction, which results in the conversion of a tetrazolium salt (iodonitrotetrazolium; INT) into a red formazan product. The reaction involves conversation of lactate to pyruvate by LDH and reduction of NAD+ to NADH. The diaphorase in presence of NADH, reduces INT (a tetrazolium salt) and generates a red color formazan. The amount of formazan formed is proportional to the amount of LDH released in the medium and the absorbance can be measured at 490nm, using a spectrophotometer or a 96-well plate reader.