The cardiovascular responses induced by intracerebroventricular or intravenous administration of ketanserin in normotensive rats were evaluated. Ketanserin, which is an antagonist at 5-HT2 receptors, when microinfused into the third cerebral ventricle, did not induce significant cardiovascular effects, except for a slight and transitory hypotensive response after the microinfusion of the highest dose (200 micrograms). However, at doses which were unable to affect directly blood pressure or heart rate, ketanserin, microinfused into the same site, antagonized the pressor response induced by peripheral administration of methoxamine, an alpha 1-adrenoceptor agonist. Furthermore, peripheral administration of ketanserin produced dose-dependent hypotension and bradycardia and antagonized the pressor effect of an intravenous bolus injection of methoxamine. In conclusion, the present experiments confirmed the ability of ketanserin to produce cardiovascular effects when administered peripherally and provides evidence for an involvement of ketanserin-sensitive receptors in the brain in the regulation of phasic responses during experimentally induced hypertension.