Cell death occurs by one of two mechanisms: apoptosis (programmed cell death) or necrosis due to cellular injury or trauma. Each method has distinct morphological and biochemical characteristics. Distinguishing between apoptosis and necrosis depends selection of appropriate assays and proper timing. This unit provides an extensive series of assays that measure membrane integrity, cell size and DNA content, state of chromatin, DNA fragmentation, and caspase activation. The results of these assays allow one to distinguish between apoptosis and necrosis.