Apoptosis is related to many diseases and induced by a family of cell death receptors. Cell death signals are transduced by DD-, DED-, or CARD-containing molecules and members of the caspase family of proteases. These death signals finally cause the degradation of chromosomal DNA by activated DNase DFF40/CAD, which is chaperoned and inhibited by DFF45/ICAD. DFF45 related proteins CIDE-A and CIDE-B (for cell death-inducing DFF-like effector A and B) were recently identified. CIDE contains a new type of domain termed CIDE-N, which has high homology with the regulatory domains of DFF45/ICAD and DFF40/CAD. Expression of CIDE-A induces DNA fragmentation and activates apoptosis, which is inhibited by DFF45. CIDE-A is expressed in many tissues.