Previous data from our laboratory showed that 344 Fisher rats fed with a protein deficient diet presented a slight increase in mean arterial blood pressure (MAP). It has been suggested in the literature that the renin-angiotensin system (RAS) could be affected by dietary restriction. This work evaluated the alterations in MAP and heart rate (HR) of Fisher rats fed for 35 days after weaning with regular (15%) or low (6%) protein diets, before and after systemic administration of the angiotensin converting enzyme inhibitor (iACE) or AT1 receptor antagonist. Under ketamine (80 mg/kg) plus xylazine (7 mg/kg) anesthesia, polyethylene cannulas were inserted into the femoral artery to record arterial pressure and into the vein for drug injections one day before the experiments. All procedures and experimental protocols were conducted in accordance with the Brazilian Society for Neuroscience and Behavior instructions for the use of animals in research. MAP levels in malnourished rats were greatly dependent on RAS because the inhibition of angiotensin converting enzyme with enalapril or the blockade of AT1 receptors with losartan produced greater fall in the blood pressure of malnourished rats compared to control rats (-37±4 mmHg vs. -3±2 mmHg, n=8 and -41±5 mmHg vs. -3±1 mmHg, n=8, respectively). To further investigate the relative contributions of angiotensin II acting directly on smooth muscle cells versus through the sympathetic nervous system to maintain blood pressure in malnourished rats, experiments were carried out with peripheral α1 adrenergic and AT1 receptors blockade. The blockade of α1 receptors with prazosin after losartan further decreased the MAP in both groups (-29±7 mmHg in control, n=8 and -17±7 mmHg in malnourished, n=8). Prazosin was less effective than losartan to reduce MAP in malnourished rats when compared to control rats that underwent the same treatment judged by the changes due to AT1 blockade versus AT1 plus α1 blockade (-8±3 mmHg and -29±4 mmHg respectively in control, n=8 vs. -44±5 mmHg and -17±7 mmHg respectively in malnourished, n=8). When prazosin was given first, malnourished rats also presented greater fall in MAP compared to control (-38±3 mmHg vs -8±2 mmHg respectively). The subsequent administration of losartan produced further and similar fall in MAP for both groups (-25±3 mmHg in control and -22±4 mmHg in malnourished). The present results suggest that ongoing production of angiotensin II and its action on AT1 receptors are critical factors supporting the blood pressure in malnourished rats and that α1 receptors activation could be under strong influence of angiotensin II.