Cayman's WST-8 Cell Proliferation Assay provides an easy to use tool for studying the induction or inhibition of cell proliferation in any in vitro model. The assay is based on the extracellular reduction of WST-8 by NADH produced in the mitochondria via trans-plasma membrane electron transport and an electron mediator. Reduction of WST-8 produces a water-soluble formazan dye which dissolves directly into the culture medium, eliminating the need for an additional solubilization step. WST-8 is more stable and less cytotoxic than the other tetrazolium salts, making it especially useful for longer incubation periods. The detection sensitivity is higher than that for other tetrazolium salts.