Thiazoyl blue tetrazolium bromide is widely used in cell biology and microbiology as a vital stain to assess cell viability and proliferation. It is particularly valuable in assays that measure mitochondrial activity in living cells. When added to cell cultures, it is reduced by metabolically active cells to formazan, a purple-colored product, which can be quantified spectrophotometrically. This property makes it a key component in cytotoxicity tests, drug screening, and studies evaluating the effects of various compounds on cell health. Additionally, it is employed in research focused on cancer cell behavior, stem cell differentiation, and microbial viability, providing a reliable and straightforward method to monitor cellular metabolic activity.