Withaferin-A-induced apoptosis in human leukemia (HL-60) cells was associated with ROS-mediated activation of both intrinsic and extrinsic pathways as shown by the induction of Bax, decreased mitochondrial membrane potential and release of cytochrome-c, activation of caspase-9, -3 and -8, and the cleavage of PARP. This evidence concerns the gene CASP9 and leukemia.