Carotid and aortic chemoreceptor function was studied in normal Wistar rats. Sodium cyanide, lobeline HCl, and doxapram HCl in the doses of 2-400 mug/kg injected into the external carotid artery stimulated respiration significantly. Injections of the drugs into the ascending aorta produced less effects which were abolished after section of the carotid sinus nerves. The drugs produced a significant increase in the carotid sinus nerve activity but failed to do so in the aortic depressor or recurrent laryngeal nerves. These results indicate that the carotid chemoreceptor function in Wistar rats in normal while functional aortic chemoreceptors are absent in them.