NutriCulture Cell Viability Detection Kit-8 (CVDK-8) allows very convenient assays by utilizing its highly water-soluble tetrazolium salt. WST-8 [2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium, monosodium salt] produces a water-soluble formazan dye upon reduction in the presence of an electron mediator. NutriCulture CVDK-8 is a one-bottle solution; no premixing of components is required. NutriCulture CVDK-8, allows sensitive colorimetric assays for the determination of the number of viable cells in cell proliferation and cytotoxicity assays. WST-8 is reduced by dehydrogenases in cells to give an orange colored product (formazan), which is soluble in the tissue culture medium. The amount of the formazan dye generated by dehydrogenases in cells is directly proportional to the number of living cells. The detection sensitivity using NutriCulture CVDK-8 is higher than assays using other tetrazolium salts such as MTT, XTT, MTS or WST-1.