This study was performed to determine whether, in hypertensive and normotensive rats, chronic sympathetic denervation impairs cerebral vasodilator responses during hypotension, and to determine whether there are regional differences in the autoregulatory response of brain vessels during hypotension. The superior cervical ganglion was removed on one side in stroke-prone spontaneously hypertensive rats (SHRSP) and normotensive (WKY) rats. Cerebral blood flow (CBF) was measured with microspheres when the rats were 5–6 months old. Chronic sympathetic denervation had little or no effect on cerebral vasodilator responses during acute hypotension in SHRSP and WKY. We suggest that the increase in incidence of ischemic infarction that we have observed previously after chronic sympathetic denervation in SHRSP probably is not the result of ischemia during episodes of hypotension. We also observed major regional differences in the response of cerebral vessels during acute hypotension in SHRSP: blood flow to brainstem was preserved better than flow to cerebrum and cerebellum. Thus the “lower limit” of the autoregulatory plateau differs in various regions of the brain in SHRSP.