The role of sino-aortic reflexes in the control of circulation during normal behavior was investigated by comparing cardiovascular reactions during various but reproducible types of behavior before and after bilateral sino-aortic deafferentation. Chronic deafferentation caused little change in baseline blood pressure, but a subtler, important role of sino-aortic reflexes was revealed by examining the integrated cardiovascular responses to behavioral stimuli. During desynchronized sleep, the buffering action of sino-aortic reflexes prevented a marked and diffuse vasodilation, with an action that was particularly evident on muscle blood vessels. During emotional behavior, especially when emotion was accompanied by movement, sino-aortic reflexes opposed the consequences of muscle vasodilation by inducing tachycardia and vasoconstriction in the viscera and in noncontracting muscles. A reciprocal type of interaction between behavior and sino-aortic reflexes was shown by testing the amplitude of the carotid occlusion response before and during desynchronized sleep; the latter condition was consistently associated with decreased effectiveness of the reflex response. The possibility is considered that this might indicate central suppression of the carotid sinus reflex during desynchronized sleep and that a similar inhibitory interference might occur during emotional behavior. Alternatively, reduction of the reflex response might result from a shift of the stimulus-response curve on either side of its steep portion.