The effects of intracerebroventricular administration of bombesin on mean arterial pressure and heart rate were studied in conscious, freely moving rats. Injection of bombesin produced dose-dependent elevations of mean arterial pressure and reductions of heart rate. These effects were not caused by leakage of bombesin into the peripheral circulation. Adrenalectomy abolished the pressor action of bombesin but did not alter bombesin-induced bradycardia. Systemic phentolamine pretreatment prevented bombesin-induced changes of mean arterial pressure, whereas rats treated intravenously with captopril or a vasopressin antagonist still exhibited pressor responses to bombesin administration. Bombesin-induced bradycardia was partially antagonized by intravenous atropine methyl nitrate administration, whereas systemic injections of propranolol did not modify this response. It is concluded that bombesin acts within the central nervous system to elevate mean arterial pressure through an adrenal-dependent mechanism involving alpha-adrenergic receptors and to reduce heart rate through an adrenal-independent mechanism involving, at least in part, cardiac parasympathetic nervous activation.