p-Tolyltetrazolium Red is primarily used as a redox indicator in biochemical assays, particularly in cell viability and cytotoxicity studies. It is commonly applied in tetrazolium reduction assays, where it is reduced by metabolically active cells (via dehydrogenase enzymes) to form a colored formazan product, allowing researchers to quantify cell proliferation or toxicity. This chemical is also utilized in microbiology to assess microbial activity and in plant physiology to study seed viability. Its ability to change color in response to cellular metabolic activity makes it a valuable tool in various biological and medical research applications.