1. The role of circulating bradykinin in blood pressure regulation was studied in conscious spontaneously hypertensive rats utilizing the competitive antagonist of bradykinin B4162. 2. This antagonist was administered at a bolus dose (400 micrograms i.v.) known to block the hypotensive effect of exogenous bradykinin for at least 2 min. The rats were maintained for 10 days either on a low or a high sodium intake. 3. The antagonist of bradykinin significantly increased blood pressure only in salt-depleted rats. In other rats kept on a low or a high sodium intake, dose-response curves to exogenous bradykinin were established. Dietary sodium had no influence on the blood pressure-lowering effect of bradykinin. 4. These data therefore suggest that circulating bradykinin may be involved in the blood pressure control of spontaneously hypertensive rats when the renin-angiotensin system is stimulated by salt depletion.