Arterial blood pressure (BP) and heart rate (HR) were continuously recorded during lateral hypothalamic self-stimulation with optimal stimulus parameters in rats. Hyper-hypotensive, hypertensive and hypotensive reactions were observed during separate self-stimulation, and the biphasic type considerably prevailed over other types of reactions. During the single cycles of self-stimulation hyper-hypotensive and hypertensive reactions with different heart rate reactions also occurred. In this case the biphasic type was seen in 75% of all reactions, whereas the hypotensive type occurred in 25% of the cases. The main type of BP reaction (92%) during continuous self-stimulation for 60-240 min was a gradual increase of the mean BP level from 15 to 40 mm Hg against initial values (p less than 0.001), that depended on the duration of self-stimulation. Changes of HR were more variable: tachycardia and bradycardia were seen approximately with the same frequency. Comparative analysis of cardiovascular reactions during hypothalamic SS and escape reactions provoked by ventromedial hypothalamus stimulation revealed some peculiarities of autonomic manifestations during positive and negative emotional reactions. The results of this comparison raises the question of a stress-reaction during self-stimulation behaviour.