5-Cyano-2,3-di-(p-tolyl)tetrazolium chloride is primarily used in biochemical assays as a redox indicator. It is particularly valuable in cell viability studies, where it helps to assess the metabolic activity of cells. When introduced to a cellular environment, this compound is reduced by metabolically active cells, leading to a color change that can be quantified spectrophotometrically. This makes it a useful tool in research settings for evaluating the effects of drugs, toxins, or other treatments on cell health and proliferation. Additionally, it is employed in microbiology for detecting bacterial growth and in enzyme activity assays to monitor redox reactions. Its sensitivity and specificity make it a reliable choice for various laboratory applications.