Programmed cell death 6 (PDCD6) protein is a 22 kDa EF-hand type Ca2+-binding protein involved in apoptosis. To define the regulating mechanism of PDCD6 activity in the apoptotic pathway, we searched a human ovary cDNA library for a novel PDCD6 binding protein using a yeast two-hybrid system. The selected protein was the human death-associated protein kinase 1 (DAPk1), another protein that functions as a positive mediator of apoptosis. Co-transfection of PDCD6 and DAPk1 cDNA into a tumor cell line accelerated apoptosis via caspase-3 dependent pathway.