The effect of angiotensin II (5, 10 and 20 ng/kg X min) on blood pressure and on the plasma concentrations of aldosterone was studied in 6 healthy men with and without the concomitant administration of a bolus-primed infusion (t = 6 h) of synthetic human atrial natriuretic peptide (hANP; experiment I: bolus of 25 micrograms followed by an infusion of 25 micrograms/h; experiment II: bolus of 175 micrograms followed by an infusion of 100 micrograms/h). The pressor effect of angiotensin II (i.e.: the rise of mean blood pressure above individual basal levels) remained unchanged during the administration of both doses of hANP. The angiotensin II-induced rise in plasma concentrations of aldosterone was reduced by hANP during both trials. Hence, the therapeutical impact in hypertensive patients might, in part, be mediated via reduction of high aldosterone concentrations.