The effects of intracerebroventricular injection of atrial natriuretic polypeptide (ANP) and angiotensin II (AII) on the concentration of dopamine, noradrenaline, serotonin and their primary metabolites in the rat brain were studied using high performance liquid chromatography with electrochemical detection. ANP (2 and 5 micrograms) decreased the level of dopamine and its metabolite in the septum and hypothalamus. In contrast, AII (100 ng) increased their levels in these brain regions. The simultaneous administration of ANP (5 micrograms) with AII (100 ng) resulted in a marked reduction of the AII-induced increase of dopamine and its metabolite. No significant changes were observed in the concentrations of noradrenaline and serotonin throughout the brain. These results suggest that the central action of ANP is mediated in part via the dopaminergic system.