The responsiveness of plasma aldosterone to an angiotensin (Ang) II infusion was assessed in normotensive young men, nine without and 13 with a family history of essential hypertension, after 7 days of low (mean urinary sodium 12 ± 10 mmol/24 h) and 7 days of high (269 ± 92 mmol/day) sodium intake. Under both conditions, the two study groups did not differ in body weight, arterial pressure, heart rate, plasma or urinary sodium and potassium or plasma renin, aldosterone or Ang II levels. However, after both dietary periods, the relationship between plasma aldosterone and plasma Ang II concentrations had shifted significantly (P< 0.01) to the right in predisposed compared to non-predisposed subjects. The sodium-related changes in adrenocortical sensitivity to Ang II were similar in the two groups. The pressor response to Ang II did not differ between the two groups of subjects. These findings suggest that, in addition to the known cardiovascular abnormalities of sympathetic, renal and ion transport mechanisms, a fourth area of disturbance involving the response of plasma aldosterone to Ang II may be present in normotensive subjects with familiar predisposition to essential hypertension.