1. In the early phase of hypertension produced by renal artery constriction with the opposite kidney intact, infusion of the angiotensin antagonist Sar1-Ala8-angiotensin II or bilateral nephrectomy lowered blood pressure. However, the extent of the fall was variable and some animals remained hypertensive after each procedure. 2. To assess whether sodium retention was the additional factor which maintained blood pressure when the renin-angiotensin system was suppressed, rats were maintained on a low-salt diet before and during the development of hypertension. The blood pressure-lowering effect of bilateral nephrectomy or antagonist infusion was not enhanced. 3. Infusion of antagonist or converting-enzyme inhibitor 6 h after bilateral nephrectomy had only a minor blood pressure-lowering action, indicating that, at this late stage after nephrectomy, the renin-angiotensin system makes only a very small contribution to blood pressure maintenance.