During perfusion with a glucose concentration of 150 mg/100 ml, infusions of l-epinephrine, l-norepinephrine, and d-l-isoproterenol at physiological concentrations of 2 ng/ml for 9 min stimulated secretion of glucagon in a monophasic response pattern, in contrast to the biphasic response normally encountered after glucagon releasing stimuli as previously reported from our laboratory (1971. J. Clin. Invest.50: 2123). Glucagon was stimulated in spite of a glucose concentration which in itself effectively inhibits glucagon release. Release of insulin was strongly inhibited after epinephrine and norepinephrine, and strongly stimulated after isoproterenol. During perfusion with a glucose concentration of 25 mg/100 ml, secretion of glucagon was greatly accentuated by the catechols investigated. Secretion of insulin remained unchanged after epinephrine and norepinephrine, but was stimulated by isoproterenol. The catechol induced glucagon release was suppressed or abolished when the beta-blocking agent propanolol was simultaneously infused at a concentration of 1 muM, while the inhibition of insulin became further accentuated. The catechol induced glucagon release remained unchanged when alpha blockade was performed using either phentolamine (1 muM) or dibenzyline (10 mug/ml), while the inhibition of insulin was converted to a stimulation. Evidence is thus presented that both the alpha cells and the bet cells are under the influence of adrenergic substances, the stimulation of glucagon release being mediated through a beta receptor and the inhibition of insulin release being mediated through an alpha receptor.