Cell Proliferation Assay Kits ATCC Cell Proliferation Assay kits are convenient and valuable tools for the quantitative evaluation of a cell population's response to external factors that affect cell viability and growth. MTT Cell Proliferation Assay Kit Utilizes the most widely accepted detection reagents, tetrazolium salts, for the safe, accurate, and straightforward quantification of changes in cell proliferation. Among the applications are drug sensitivity, cytotoxicity, response to growth factors, and cell activation. XTT Cell Proliferation Assay Kit Utilizes the second generation tetrazolium dye, XTT (sodium 2,3,-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino)-carbonyl]-2H-tetrazolium inner salt), to measure cell growth, cytotoxicity, and apoptosis. It is a homogenous, highly sensitive, reproducible assay, and adaptable to high-throughput screening.