The purpose of this study was to determine the effects of long-term consumption of tobacco smoke on arterial blood pressure regulation. Male Sprague-Dawley rats were administered tobacco smoke for 6-8 mo. Two groups of animals (A and B) received tobacco smoke containing different levels of nicotine (group A: high nicotine, 4 mg/cigarette; group B: low nicotine, 1 mg/cigarette), while a third group (C) served as a sham control by receiving only puffs of room air. Reflex adjustments in mean arterial blood pressure (MAP), heart rate (HR), lower body blood flow, and lower body vascular resistance were compared between the three groups. In the anesthetized control state, no significant difference existed for the cardiovascular parameters measured in the three groups. However, perturbating the cardiovascular system by reducing central blood volume via a 60 degrees head-up tilt elicited less of a fall in MAP in the two smoke groups compared with the sham group. Percent decreases in MAP follow: group A, 23%; group B, 22%; and group C, 48%. Increasing MAP with phenylephrine elicited a significantly greater (P less than 0.05) reduction in HR in groups A and B (smoke treated) compared with group C (sham treated). Finally, varying carotid sinus pressure elicited significantly greater (P less than 0.01) changes in MAP in the smoke-treated animals (A and B) compared with the sham group (C). It is concluded that chronic tobacco smoke administration to laboratory rats increases the sensitivity of the reflex control of the cardiovascular system.