INT Formazan is the insoluble, red-colored product resulting from the reduction of INT (2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyltetrazolium chloride), a tetrazolium salt used as a chromogenic substrate in biochemical assays. It is particularly valuable in cell viability and cytotoxicity studies, where the formation of INT Formazan by dehydrogenase enzymes in metabolically active cells enables quantitative assessment of cellular metabolic activity via spectrophotometry or visual inspection. This application is crucial in drug screening and toxicology research to evaluate compound effects on cell health. In microbiology, INT Formazan detection helps assess microbial activity and population dynamics in environmental samples such as soil and water. Furthermore, in histochemistry, it facilitates the visualization of dehydrogenase activity in tissue sections, providing insights into cellular processes and tissue pathology.