Chronic reversal of vertebral flow was created in 14 mongrel dogs by occlusion of the first portion of the right subclavian artery. All animals demonstrated reversal of flow of significant degree, which could be markedly increased by mild repetitive muscle contraction. The degree of reversal was directly related to delta pressure in linear fashion. Flow in the forepaw distal to the occlusion was initially decreased but rapidly returned to normal values in spite of lower blood pressure. Resistance was decreased and showed even further decrease when exposed to conditions causing reactive hyperemia. Flow-pulse ratios were high on the side of the occlusion. These factors suggest a distal autoregulation in the vascular bed. Further evaluation of these phenomena may lead to a new aid in the diagnostic investigation of patients with symptoms of vertebrobasilar insufficiency.