The present invention relates to an action between an inhibitor of apoptosis (IAP) protein and members of the caspase family of cell death proteases, for example, an interaction of the X chromosome linked IAP (XIAP) and caspase-3, caspase-7 or caspase-9, wherein the IAP regulates the activity of the caspases. The invention provides screening assays for identifying agents that alter the specific association of an IAP such as XIAP, c-IAP-1 or c-IAP-2 and a caspase such as caspase-3 or caspase-7. The invention also provides screening assays for identifying agents that alter the specific association of an IAP such as XIAP, c-IAP-1 or c-IAP-2 and a pro-caspase such as pro-caspase-9. In addition, the invention also provides methods for identifying agents that modulate the activity of a caspase in the presence of an IAP and that regulate the activation of a pro-caspase by an IAP. The invention further provides methods of reducing the severity of a pathologic condition in an individual by administering to the individual an agent that alters the caspase inhibitory activity of an IAP. In addition, the invention provides methods of modulating the ability of a population of cells to survive ex vivo by contacting the cells with an agent that alters the caspase inhibitory activity of an IAP in the cells.