It is now agreed that the cerebral circulation is regulated by intrinsic mechanisms so long as the mean arterial pressure remains above a critical minimal level. This intrinsic control is principally, if not entirely, affected by alterations in cerebrovascular resistance (CVR) through humoral mechanisms. Though a distinct cerebrovascular nerve supply has been recognized by all observers, its physiologic role is generally questioned. In man, direct studies on the influence of the sympathetic nerve supply upon the cerebral circulation have been limited to a few reports on the effect of stellate ganglion block,1-4 and my previous reports on the results of stellate ganglionectomy.5,6 In three investigations1-3 with stellate ganglion block, no influence on the cerebral circulation was demonstrated, but Linden, in 1955, reported a decrease of CVR from stellate ganglion block in patients with initially high CVR. This confirmed the previous report of such an effect from stellate