Abstract Stereotaxic injection of noradrenaline (3–100 nmol) into the anterior hypothalamicpreoptic region of pentobarbital anaesthetized rats induced a fall in blood pressure and heart rate. The size of the effect was related to the size of the dose. Phenylephrine (70 nmol) and clonidine (1.5–100 nmol), two typical alpha adrenergic receptor stimulating agents, mimicked the noradrenaline induced depressor effects. Local pretreatment with phentolamine (106 nmol) abolished the fall in blood pressure and heart rate induced by noradrenaline (40 nmol) or clonidine (15 and 40 nmol). Noradrenaline (40 nmol) and clonidine (15 nmol) injected into the brain ventricles also caused a fall of both blood pressure and heart rate, but the size of these effects was significantly smaller than that after direct intrahypothalamic injection of the same amounts of these drugs. These results suggest that stimulation of alpha adrenergic receptors in the anterior hypothalamic-preoptic region of rats causes a fall in blood pressure and heart rate. The relevance of these data is discussed in view of the role of alpha adrenergic receptors in the hypothalamus in both cardiovascular regulation and thermoregulation.