We have proposed that sodium appetite is aroused by a synergy in the brain of angiotensin II and aldosterone. This hypothesis was tested with 1) chronic intracerebroventricular infusion of captopril, which blocks the conversion of angiotensin I to angiotensin II, or 2) intracerebroventricular injection of eight-substiuted analogues of angiotensin II, which blocks its receptors. Both treatments resulted in a suppression of the sodium appetite induced by sodium deficiency. The suppression was specific for the deficiency-induced appetite, because spontaneous ingestive behaviors were not changed nor was sodium excretion. In addition, the rats continued to express a sodium appetite aroused by pharmacological doses of deoxycorticosterone acetate when they received the highest dose of chronic intracerebroventricular captopril. These results offer compelling evidence for the idea that angiotensin II action in the brain is necessary for expression of sodium appetite.