SummaryFour female and 2 male chronically nephrectomized human subjects were submitted to incremental infusions of angiotensin II before and after selective sodium depletion. The latter was achieved by dietary sodium restriction (potassium intake remaining constant) combined with weight-reducing haemodialysis. In all 6 patients, this procedure resulted in significant falls in mean blood pressure, in serum sodium concentration and in body weight, whereas serum potassium concentration was unaltered. Plasma renin concentration was within the normal range in 5 patients. Plasma angiotensin II concentration was within the normal range in all cases. Both renin and angiotensin II concentrations were unaltered by selective sodium depletion.When angiotensin II was infused intravenously at doses of 1, 2, 4 and 8 ng kg min for Heach, pressor dose-response curves were obtained by plotting the increases in mean blood pressure against the log of the corresponding arterial plasma angiotensin II concentrations. The curves obtained prior to and after sodium depletion were not significantly different.However, when absolute figures of mean blood pressure were plotted against the corresponding plasma angiotensin II concentrations, a downward shift of the curve was observed after sodium depletion. In other words, the relationship between angiotensin II and blood pressure remained the same after sodium depletion, but it took place at a lower baseline level.These relationships were compared with 2 other sets of data, namely those obtained from 5 normal subjects during incremental angiotensin II infusions before and after sodium depletion, and those obtained from 51 patients with renal hypertension after 3 days on a fixed 150 mEq sodium/day intake (21 cases) or on a normal ward diet (30 cases).In the first instance, it was observed that normal subjects, in both sodium replete or sodium deplete states, displayed a mean blood pressure-angiotensin II relationship not significantly different from that obtained in sodium-depleted anephric patients.When spontaneous values of plasma angiotensin II concentration in the 51 hypertensive patients were plotted against the corresponding basal mean blood pressures, the slope of the curve was not different from that obtained in the other groups, but the intercept was significantly higher. These data suggest:1) That sodium depletion“per se”is not able to alter pressor responsiveness to intravenously infused angiotensin II.2) That the relationship between angiotensin II and blood pressure is essentially the same in the different groups studied, but takes place at different basal blood pressure levels.3) That sodium status may be important in determining this basal level is shown by the fact that sodium-replete anephrics are intermediate between the regressions for normal and hypertensive subjects.