DOJINDO is the original creator of WST dyes and Cell Counting Kit-8 (CCK-8). CCK-8 has been used by researchers all over the world for over 20 years. The reasons for this include 1) reliable and stable quality, 2) long-term stability (1 year: 0-5°C, 2 years: -20°C), 3) higher sensitivity than MTT, XTT, MTS, or WST-1, and 4) low toxicity to cells, a combination of features that have been improved over its long history and that no other company can imitate. CCK-8 enables sensitive colorimetric assays to determine cell viability in cell proliferation and cytotoxicity assays. The kit includes Dojindo's WST-8 which is reduced by dehydrogenase activity in cells to give a yellow-colored formazan dye. The amount of the dye, generated by the activity of dehydrogenases in cells, is directly proportional to the number of living cells.