The effects of intracerebroventricular (i.c.v.) administration of ANP on blood pressure and intakes of water and salt were examined, using conscious, unrestrained normotensive Wistar rats and spontaneously hypertensive rats (SHR). In normotensive rats, i.c.v. administration of α-rat ANP (α-rANP), α-human ANP (α-hANP), α-rANP (4-28) and α-rANP (5-28) at the dose of 1.5 nmol significantly attenuated water intake induced by i.c.v. injection of 0.1 nmol of angiotensin II (AII). Centrally administered α-hANP (5 μg) also attenuated AII-induced pressor response. Centrally injected α-hANP (1 μg) produced a greater reduction of water intake after 24-hour water deprivation in SHR compared to control WInstar Kyoto rats (WKY). Central infusion of α-hANP for 1 week also reduced the salt appetite of SHR, as shown by two bottle preference test with 0.3 N NaCl solution and tap water, while it had no effect on drinking behavior of WKY. These results suggest the central antagonistic relationship of the ANP and renin-angiotensin systems and the possible involvement of brain ANP in the pathophysiology of genetically hypertensive rats.