A proper rate of programmed cell death or apoptosis is required to maintain normal tissue homeostasis. In disease states such as cancer and some forms of hypertension, apoptosis is blocked, resulting in hyperplasia. In neurodegenerative diseases, uncontrolled apoptosis leads to loss of brain tissue. The flow of ions in and out of the cell and its intracellular organelles is becoming increasingly linked to the generation of many of these diseased states. This review focuses on the transport of K(+) across the cell membrane and that of the mitochondria via integral K(+)-permeable channels. We describe the different types of K(+) channels that have been identified, and investigate the roles they play in controlling the different phases of apoptosis: early cell shrinkage, cytochrome c release, caspase activation, and DNA fragmentation. Attention is also given to K(+) channels on the inner mitochondrial membrane, whose activity may underlie anti- or pro-apoptotic mechanisms in neurons and cardiomyocytes.