Activation of caspases plays a central role in apoptosis. The CaspGLOW™ Fluorescein Active Caspase-3 Staining Kit provides a convenient means for sensitive detection of activated caspase-3 in living cells. The assay utilizes the caspase-3 inhibitor, DEVD-FMK, conjugated to FITC (FITC-DEVD-FMK) as a marker. FITC-DEVD-FMK is cell permeable, nontoxic, and irreversibly binds to activated caspase-3 in apoptotic cells.