Although agonist-induced desensitization of adrenergic receptors has been previously demonstrated, the regulation of adrenergic receptors during acute psychological stress has not been investigated in humans. We studied 30 first year medical students during final examination week and one month earlier. Platelet alpha 2 receptor binding was measured using 3H-yohimbine and leukocyte beta 2 receptor binding was measured with 125I-CYP (Iodocyanopindolol). During final examination week, platelet alpha 2-receptor binding affinity was significantly reduced, while levels of plasma catecholamines and reported anxiety were significantly increased, compared with the earlier period. Students showing the greatest increases in plasma norepinephrine and in reported anxiety also demonstrated the greatest reductions in alpha 2 receptor binding affinity. These data show that acute psychological stress can produce adrenergic receptor desensitization, possibly through increased levels of circulating norepinephrine.