Used primarily in biological assays to measure cell viability and metabolic activity. It acts as an indicator in tetrazolium-based assays, where living cells reduce it to a colored formazan product, allowing quantification of cellular metabolism. Commonly applied in cytotoxicity, proliferation, and drug screening studies. Its reduction occurs mainly by dehydrogenase enzymes in active mitochondria, making it a marker for functional cell health. Suitable for high-throughput screening due to its sensitivity and ease of detection with spectrophotometers.