1. Total exchangeable sodium was measured in rats by a radio-sodium equilibration method, before and after the production of hypertension by clipping the left renal artery, with or without contralateral nephrectomy.
2. Clipping of one renal artery with removal of the other kidney produced severe hypertension with no significant changes in exchangeable sodium or plasma renin levels.
3. Clipping of one renal artery without contralateral nephrectomy produced severe hypertension in some animals, but little change in blood pressure in others. The animals which developed severe hypertension had a marked increase in exchangeable sodium with a concomitant rise in plasma renin; the animals with smaller rises in blood pressure did not have these changes.
4. The fact that both plasma renin levels and exchangeable sodium levels increase according to this method, suggests that hypertension in the two-kidney model is renin-dependent.