Apoptosis is related to many diseases and induced by a family of cell death receptors and their ligands. Cell death signals are transduced by death domain containing adapter molecules and members of the caspase family of proteases. These death signals finally cause the degradation of chromosomal DNA by activated DNase. DFF45/ICAD has been identified as an inhibitor of caspase activated DNase DFF40/CAD. DFF45 related proteins CIDE A and CIDE 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 B induces apoptosis, which is inhibited by DFF45. CIDE B is a DFF45 inhibitable effector that promotes cell death and DNA fragmentation. CIDE B is expressed mainly in liver and small intestine and at lower levels in spleen, colon, kidney, peripheral blood lymphocytes, and bone marrow.