Activation of caspases plays a central role in apoptosis. The CaspGLOWTM Red Active Caspase-3 Staining Kit provides a convenient means for detecting activated caspase-3 in living cells. The assay utilizes the caspase-3 inhibitor DEVD-FMK conjugated to sulfo-rhodamine (Red-DEVD-FMK) as the fluorescent in situ marker. Red-DEVD-FMK is cell permeable, nontoxic, and irreversibly binds to activated caspase-3 in apoptotic cells.