Molecular genetic study of Caenorhabditis elegans revealed the cell death-executing gene ced-3. Structural and functional similarities between CED-3 and mammalian ICE family (caspase) gene products provide the evidence that mammalian caspases are common mediators in executing programmed cell death. These findings suggest that the execution mechanisms of cell death by caspase family protease may be evolutionarily conserved from worms to mammals. This report summarizes the unique properties of caspases in apoptosis.