Activation of caspases plays a central role in apoptosis. The CaspGLOWTM Red Active Caspase-8 Staining Kit provides a convenient means for detecting activated caspase-8 in living cells. The assay utilizes a caspase-8 inhibitor IETD-FMK conjugated to sulfo-rhodamine (Red-IETD-FMK) as the fluorescent marker. Red-IETD-FMK is cell permeable, nontoxic, and irreversibly binds to activated caspase-8 in apoptotic cells.