WST-8 Cell Quantification Assay involves a simple, ready-to-use solution that can be used for the robust and high-throughput quantification of viable cell numbers. WST-8 Cell Quantification Assay solution can be directly added to cells and measured using a standard microplate reader within 1 - 4 hours. Mechanistically, this assay exploits the ability of the non-toxic tetrazolium salt, WST-8, to be reduced by cellular dehydrogenases, mediated by the electron carrier 1-methoxy-5-methylphenazinium methyl sulfate, into a water-soluble orange formazan dye. The amount of orange formazan product generated is directly proportional to the number of viable cells and can be quantified by measuring absorbance readings at 460 nm. Owing to the stability of the solution, this cell quantification assay can be used for protocols requiring longer incubation times ranging from 24 - 48 hours, with detection sensitivity being higher compared to the other tetrazolium salt-based assays, such as MTT, XTT or MTS.