1. The relationship between circulating plasma angiotensin II and plasma aldosterone in man during sodium deficiency has been investigated in normal male subjects by comparing the amounts of the two hormones: (a) after 5 days of sodium restriction with an injection of frusemide on the third day, (b) during intravenous infusions of angiotensin II given in normal sodium balance.
2. The results show that aldosterone and angiotensin II plasma concentrations were both increased by sodium deficiency, but the increase in aldosterone was much greater than was found when angiotensin II was infused during normal sodium balance so as to equal or even exceed the plasma angiotensin II concentrations of sodium deficiency.
3. Other factors capable of increasing aldosterone secretion (plasma Na+, K+ and ACTH) seemed unlikely to account for the discrepancy, nor was there evidence of sufficient increase in adrenal sensitivity during Na+ deficiency.
4. It is suggested that some other unknown factor or factors are necessary to account for the full aldosterone response to this stimulus in man.