Activation of caspases plays a central role in apoptosis. The CaspGLOW™ Fluorescein Active Caspase-8 Staining Kit provides a convenient means for sensitive detection of activated caspase-8 in living cells. The assay utilizes the caspase-8 inhibitor, IETD-FMK, conjugated to FITC (FITC-IETD-FMK) as a fluorescent in situ marker. FITC-IETD-FMK is cell permeable, nontoxic, and irreversibly binds to activated caspase-8 in apoptotic cells.