We studied the effects of intracerebroventricular administration of angiotensin II (ANG II), bradykinin (BK), leucine-enkephalin (Leu-ENK) and neurotensin (NT) on plasma renin activity (PRA), blood pressure and heart rate in conscious and unrestrained rats. Five microliters of each peptide solution was injected into the lateral cerebral ventricle. These four peptides all produced pressor effects after intracerebroventricular injection. ANG II and NT significantly suppressed PRA, BK did not affect PRA, and Leu-ENK significantly increased PRA. The central peptidergic stimulation caused by these four peptides increased blood pressures in conscious rats but showed different effects on PRA.