Studies by electrophoretic administration of NE directly at the site of extra-cellular unit recording have shown the presence of NE-sensitive units in all regions of the mammalian central nervous system thus far explored. These include the lumbar segments of the spinal cord, the medulla, the hypothalamus, the thalamus, the hippocampus, the red and caudate nuclei, the septum, and the cortex in the cat, and the olfactory bulb in the rabbit. Most responsive cells are depressed by NE but others are consistently facilitated. Irrespective of their direction, NE responses have a long latency of onset and a long duration; these features could result from dendritic sites of drug action. There is evidence that NE is a synaptic transmitter in an inhibitory pathway in the rabbit olfactory bulb.