ATP-sensitive potassium channels are found in a number of different tissues where they undertake distinct physiologic functions. In endocrine cells they regulate the secretion of hormones such as insulin, prolactin, and growth hormone. They influence the excitability of cardiac, skeletal, and vascular smooth muscle. They are of particular importance during ischemia in both the heart and the brain, where they intervene to reduce or delay cell death. Both electrophysiologic and pharmacologic evidence points toward ATP-sensitive potassium channels making up a class of ion channels with tissue-specific as well as functional differences. There is therefore considerable scope for the development of specific products to either enhance or inhibit the action of these ion channels under different pathologic conditions.