Tetraethylammonium chloride is a quaternary ammonium compound which blocks the transmission of nervous impulses across autonomic ganglions. Acheson and Moe1 first demonstrated this ganglionic site of action in dogs and cats, using as test responses the reactions of the blood pressure, heart rate and nictitating membrane. They demonstrated that when the compound is injected intravenously it produces a prompt fall in arterial pressure in animals in which the arterial pressure is elevated from the increase in sympathetic tone of barbiturate anesthesia. After section of the cervical cord in such animals the sympathetic tone is abolished, and the drug then fails to produce further change in pressure. With restoration of the pressure and vascular tone by stimulation of the distal segment of the sectioned cervical cord the administration of the drug again produces a fall in pressure to the same level as that found in the absence of sympathetic tone.