Caspase-3 has been extensively studied and implicated to play an important role in apoptosis. Active caspase-3 proteolytically cleaves and activates other caspases, as well as relevant targets in the cells (e.g., PARP). The affinity purified antibody recognizing the active forms of caspase-3 provides a new tool for identifying apoptotic cell populations in both tissue sections and cultured cells.