The intracarotidal injection of some bet-adrenergic blocking agents (dl-acebutolol, dl-, l-, d-alprenolol, dl-bunitrolol, dl-buthoxamine, dl-, l-, d-INPEA, dl-Ko 592, dl-metoprolol, dl-oxprenolol, dl-propranolol, dl-tolamolol) in anesthetized and bivagotomized dogs reduced the arterial blood pressure and the baro- and chemoreceptor activity. These effects seem to be mediated by an interaction with central nervous, cardiovascular and respiratory structures dependent on the carotid arteries and by a direct interference of these drugs with the carotid sinus baro- and chemoreceptor structures. Moreover, these effects were not a result of the beta-adrenolytic properties of the drugs.