The invention provides methods and compositions relating to novel human cellular inhibitor of apoptosis proteins (c-IAP1/2) comprising a series of defined structural domain repeats and/or a RING finger domain; in particular at least two of: a particular first domain repeat, a particular second domain repeat, and a particular third domain repeat, and/or a particular RING finger domain. The proteins provide a c-IAP specific function, with preferred proteins being capable of modulating the induction of apoptosis, for example, by binding a human tumor necrosis factor receptor associated factor (TRAF). The compositions include nucleic acids which encode the subject c-IAP and hybridization probes and primers capable of hybridizing with the disclosed c-IAP genes. The invention includes methods of using the subject compositions in therapy, in diagnosis and in the biopharmaceutical industry.