Caspase-3 is a ubiquitously-expressed cysteine protease involved in programmed cell death (apoptosis). In nonapoptotic cells, this enzyme exists as an inactive zymogen known as procaspase-3. Intracellular procaspase-3 is activated when cells are committed to die via apoptosis; induction of the cell death machinery eventually triggers activation of the zymogen by proteolytic cleavage of the zymogen to an active heterodimer comprised of 17 kDa and 12 kDa subunits. The active enzyme cleaves a number of intracellular protein targets important for cell survival. Therefore, monitoring caspase-3 enzyme activity is a fundamental means to measure apoptosis in cells. This assay is an important tool for apoptosis research as well as investigating the apoptotic effects of experimental drug formulations and cell transfection. The MaxDiscovery™ Caspase-3 Colormetric Detection Kit is a colorimetric microplate-based assay to directly measure caspase-3 activation in cultured cells. This kit enables biomedical researchers to determine caspase-3 levels in cultured cells from a broad range of cell lines. The assay utilizes a simple, proven enzymatic assay to detect activated enzyme. Because caspase-3 is expressed in every cell type, the assay can be performed using any mammalian cell line.