MANY INVESTIGATIONS of the regulation of cerebral blood flow (CBF) have been reported during the past three decades. Some of these explored the possibility of a primary neurogenic control.1-3 In the past, measurements were made of the diameter of the cerebral blood vessels4instead of the actual flow because there existed no method for measuring the latter at that time. However, in 1948, Kety and Schmidt5devised a reliable method of measuring the CBF in humans, based on Fick's principle and employing inhalations of nitrous oxide. The authors modified this method for use in dogs and demonstrated the reliability of the modification by obtaining highly significant correlations between CBF and body temperature at a level ofP6we reported that in normal dogs after bilateral superior cervical sympathetic ganglionectomy there was a decrease in the CBF rather than an expected