alpha(1)-Adrenergic receptors (ARs) mediate some of the main actions of the natural catecholamines, adrenaline and noradrenaline. They participate in many essential physiological processes, such as sympathetic neurotransmission, modulation of hepatic metabolism, control of vascular tone, cardiac contraction, and the regulation of smooth muscle activity in the genitourinary system. Here, we review recent progress on subtype-specific subcellular localization, participation in signaling cascades, and the pivotal function of alpha(1)-ARs, as delineated through studies on genetically engineered animals. Together, these findings will provide new insights into the physiological and pathophysiological roles of the alpha(1)-ARs.