Regulation of aldosterone secretion by sodium chloride is impaired in a group of essential hypertensives: high-salt diet fails to suppress aldosterone in these patients despite low renin values. The mechanism of this impaired regulation of aldosterone has not been clarified so far. We tested the sensitivity of aldosterone secretion and blood pressure to A II in 20 normotensive controls (aged 20-60, MAP 92 +/- 3 mm Hg), in ten normotensives with one or two parents with hypertension, and in 21 patients with essential hypertension (aged 17-65, MAP 119 +/- 4 mm Hg). After a period of 6 days on high-salt intake (300-320 mEq Na+/day), A II (0.1, 0.5, 1.0 and 2.0 ng/kg/min) was infused, each concentration for 30 min. According to aldosterone excretion during sodium loading, patients were divided into group A with complete suppression (n = 12, aldosterone excretion 3.6 +/- 0.4 microgram/day) and in group B with insufficient suppression (n = 9, aldosterone excretion 15.5 +/- 2.3 micrograms/day). Despite similarly low plasma renins, rise of serum aldosterone levels during A II infusion was significantly higher in group B patients than in group A patients and normotensive controls. Rise in mean arterial blood pressure, however, brought about by graded A II infusion was similar in both groups of hypertensives and in normotensive controls. The results demonstrate an increased adrenal sensitivity to A II in a subgroup of essential hypertensives only. A similar adrenal hypersensitivity to A II found by others in patients with hyperaldosteronism due to adrenal hyperplasia supports the hypothesis that the same mechanism underlies both disorders.