Epinephrine (25 ng/kg/min I.V.), administered to normal males causes a marked change in the plasma corticoid concentration curves obtained during maximal stimulation with corticotrophin (ACTH). This finding is not observed in females. The altered pattern described in the male subjects is due to a significant increase of the removal rate without a concomittant change in the production rate, resulting in a decrease of the plateau and the C8 corticoid concentration. An augmented cortisol storage outside the readily miscible distribution volume could be responsible for this increased removal rate. The administration of norepinephrine (120 ng/kg/min I. V.) causes an increase in the production rate during ACTH stimulation in normal males and females. As indicated by the unchanged level of urinary cortisol metabolites, there is no change in the total production of adrenal corticoids; thus a decrease of the mean distribution volume of the readily miscible corticoids is probable. An increase of the removal rate is also observed under these circumstances in males but not in females. As to the diurnal variation of plasma corticoids during ACTH stimulation, significant quantitative and qualitative differences are found between the sexes during the evening and night. Some of these differences in males disappear after the administration of phentolamine methanesulfonate (Regitine), which suggests an interference of endogenous catecholamines in the observed phenomenon.