This study was performed in order to determine whether the stimulatory effect of plasma angiotensin II (ANG II) on Adrenocorticotropic hormone (ACTH) and growth hormone (GH) secretion in humans is mediated by AT1 subtype receptors. For this purpose, the effects of the administration of the AT1 receptor antagonist, losartan (50 mg p.o.) or a placebo on the ACTH and GH responses to ANG II (i.v. infusion for 60 min of successively increasing doses (4, 8 and 16 ng/kg/min); each dose for 20 min) were evaluated in eight normal men. ANG II infusion induced significant increases in both serum ACTH and GH levels (mean peaks were 1.6- and four-times higher than baseline, respectively). The ACTH response to ANG II was completely abolished by pretreatment with losartan. Also, the ANG II-induced GH rise was reduced by administration of losartan, but the GH response was still significantly higher than the basal value (mean peak was twice as high as the baseline). These data provide evidence of AT1 receptor involvement in mediation of the ANG-II stimulating effect on ACTH and GH secretion.