Aging decreases hormone responsiveness in several receptor systems. In this article I consider both physiological and biochemical studies supporting the hypothesis that beta-adrenergic receptor responsiveness is reduced with aging in humans. Reduced chronotropic and vasodilator responses to the beta-receptor agonists isoproterenol and metaproterenol have been demonstrated. In human leukocytes a reduction in adenylate cyclase (EC 4.6.1.1) activity occurs with aging. More recently it has been suggested that this reduction in beta-adrenergic responsiveness with aging may be caused by an uncoupling of the beta receptor from the catalytic component.