We examined the effects of intracerebroventricular (i.c.v.) administration of atrial natriuretic factor (ANF) on pressor and natriuretic responses induced by i.c.v. angiotensin II (Ang II) or hypertonic NaCI. Conscious male Wistar rats were given one of the following solutions into the lateral ventricle: artificial cerebrospinal fluid (CSF); rat ANF (99–126) 1.0 µg/kg per min; Ang II 100 ng/kg per min; 0.6 mol/l NaCI; Ang II plus ANF, and 0.6 mol/l NaCI plus ANF.The i.c.v. infusion of artificial CSF or ANF alone did not cause significant changes in mean blood pressure, urinary volume or sodium excretion (UNaV). The i.c.v. infusion of Ang II or 0.6 mol/l NaCI raised mean blood pressure, decreased urinary volume and increased UNaV. When ANF was administered with Ang II, the Ang ll-induced responses were diminished significantly (Δmean blood pressure, +10 ± 3 versus + 20 ± 4mmHg; Δurinary volume, - 38 ± 9 versus - 78 ± 5µl/min; ΔUNaV, +0.49 ± 0.51 versus + 2.28 ± 0.58 µmol/min). The centrally administered ANF opposed the effects of 0.6 mol/l NaCI, though the effect was significant only in respect of blood pressure.Our results indicate that the brain ANF may have an antinatriuretic role in some conditions. Journal of Hypertension 1989, 7:639–643