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