Cayman's WST-8 Cell Proliferation Assay provides a tool for studying induction and 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 resulting in a water-soluble formazan which dissolves directly into the culture medium. Cayman's WST-8 assay is preferred when higher cell densities are expected, as up to 5 x 106 cells/ml can be successfully quantified.