THE REGULATION of vasopressor and vesicopressor functions by the central nervous system (CNS) occurs at a series of levels, of which the highest are the hypothalamus and the cerebral cortex. Neither of these structures is indispensable for the maintenance of blood pressure, as evidenced by the normal levels that are present after decerebration at the midcollicular level. However, stimulation of the cortex, and particularly the hypothalamus, can produce marked variations in blood pressure which range from increases up to double the resting systolic pressure to decreases of 20 mm Hg or more. Numerous investigations of the hypothalamic visceromotor pathways followed the initial studies of Karplus and Kreidl.1-4A survey of this voluminous literature reveals areas of general agreement and others of controversy.5-15It is generally agreed that the most caudal part of the hypothalamus, the periaqueductal gray substance, and the midbrain tegmentum contain areas Kabat and associates12