FAM-VEID-FMK is a cell permeable inhibitor of caspase 6. It detects active caspase 6 in living cells. FAM-VEID-FMK is non-cytotoxic during the course of the assay and thus allows the detection of active caspase 6 in living cell systems. FAM-VEID-FMK irreversibly binds to active caspase 6. Caspases 3, 7 and 8 might also be labeled too, but much less efficiently than caspase 6. Caspase 6-positive cells may be identified by flow cytometry or fluorescence microscopy with fluorescent FAM-VEID-FMK. Apoptosis is an evolutionarily conserved form of cell suicide, which follows a specialized cellular process. The central component of the apoptosis process is a cascade of proteolytic enzymes called caspases. These enzymes participate in a series of reactions that are triggered in response to pro-apoptotic signals and result in cleavage of protein substrates, causing the disassembly of the cell. Caspases have been identified in organisms ranging from C. elegans to humans. The mammalian caspases play distinct roles in apoptosis and inflammation. In apoptosis, caspases are responsible for proteolytic cleavages that lead to cell disassembly (effector caspases) and are involved in upstream regulatory events (initiator caspases). An active caspase consists of two large (~20 kD) and two small (~10 kD) subunits to form two heterodimers which associate in a tetramer.