The majority of cerebral autoregulation research has focused on the middle cerebral artery. However, many symptoms of presyncope indicate posterior cerebral hypoperfusion. To address this issue, we measured cerebrovascular reactivity, cerebral blood flow velocity and dynamic cerebral autoregulation in the middle cerebral artery and vertebral arteries during orthostatic stress to presyncope in 9 healthy subjects. There was no significant difference in either the decline in cerebral blood flow velocity or indices of dynamic cerebral autoregulation between the middle cerebral and vertebral arteries prior to or during presyncope. In conclusion, there is no significant difference in regulation of blood flow between the vertebral artery and middle cerebral artery in healthy subjects. Further study is required to determine whether or not a difference exists in syncopal patient populations.