Intraventricular administration of nicotine produced a biphasic effect, consisting of an initial rise than a slight fall in blood pressure in unanaesthetized rats. Spontaneously hypertensive rate (SHR) showed increased pressor responses, but these responses were within normal limits in renal hypertensive and DOCA-saline hypertensive rats. The blood pressure response to nicotine in SHR was abolished by intraventricular administration of hexamethonium, but not by atropine given via the same route. Central phentolamine and 6-hydroxydopamine did not affect the pressor response to nicotine. The pressor effect of nicotine in SHR was markedly diminished after removal of the adrenals and abolished after bilateral adrenalectomy plus peripheral 6-hydroxydopamine. These results indicate that the pressor response to intraventricular nicotine is increased in SHR. The pressor effect of nicotine may result from the activation of the central nicotinic receptor sites, which may cause the release of catecholamines both from the adrenal medulla and adrenergic nerve terminals.