The relative effects of central and peripheral chemical stimulation of respiratory movements by NaCN were studied by intra-arterial and intravenous injection. Evidence is presented indicating that cyanide injected intra-arterially in small amounts is fixed locally by the tissues and does not reach the general circulation. Chemical stimulation should, therefore, be limited to the local distribution of the artery involved. Cyanide, sufficient to excite ventilation when injected intravenously, produced no demonstrable effects when injected at the same rate into a patent common carotid artery. If prior to injection the opposite carotid or the vertebral arteries were occluded, injection into the patent carotid artery excited ventilation. This excitation was in turn prevented by occlusion of the corresponding internal carotid. Injection of cyanide into the patent vertebral arteries elicited marked effects. It is concluded that any procedure which shunts or delivers cyanide to the lower nerve centers tends to excite ventilation, while any procedure which confines the delivery of cyanide to the head region (excluding the lower nerve centers) is unaccompanied by excitation It, therefore, appears that chemical stimulating effects of cyanide in the head region are largely, if not entirely, confined to nerve centers rather than to a peripheral nervous mechanism. The results are in agreement with other experiments on peripheral chemical stimulation of the vagus nerve endings by disturbances of oxidations.