The CytoTox 96® Non-Radioactive Cytotoxicity Assay is a colorimetric alternative to radioactive cytotoxicity assays. The assay quantitatively measures lactate dehydrogenase (LDH), a stable cytosolic enzyme that is released upon cell lysis, in much the same way as [⁵¹Cr] is released in radioactive assays. Released LDH in culture supernatants is measured with a 30-minute coupled enzymatic assay that results in the conversion of a tetrazolium salt (INT) into a red formazan product. The amount of color formed is proportional to the number of lysed cells. Visible wavelength absorbance data are collected using a standard 96-well plate reader. The assay can be used to measure membrane integrity for cell-mediated cytotoxicity assays in which a target cell is lysed by an effector cell, or to measure lysis of target cells by bacteria, viruses, proteins, chemicals, etc.

The CytoTox 96® Non-Radioactive Cytotoxicity Assay requires no radioactive waste disposal or [⁵¹Cr] and eliminates labeling of target cells prior to conducting experiments. Standard equipment can be used to collect absorbance (visible wavelength) data with a standard 96-well plate reader. The assay can be used for a variety of applications including measurement of 1) cell-mediated cytotoxicity; 2) chemical-mediated cytotoxicity; and 3) total cell number. A highly sensitive assay, it can reveal early, low-level damage to cell membranes that is often missed with other methodologies.