Although symptoms of ischemia due to arteriosclerosis obliterans may be caused by an isolated occlusive lesion, commonly, when the related portion of the arterial tree is examined by arteriography, multiple segmental lesions are detected.3 When reconstructive surgery is planned, the significance of each of these lesions must be assessed. Generally, it has been observed that when a stenosis exceeds 50% of the diameter of an artery a pressure gradient (or impairment of blood flow) can be demonstrated.5,6,9 When the lesions are separated by intervening collateral beds, repair of any one of the significant lesions usually produces improvement or relief of symptoms.8,11 However, when multiple stenoses occur in the cerebral circulation, where long, unbranched arterial segments are found, one or more lesions may lie in areas inaccessible to surgery. In this situation the problem is not so straightforward. This is because many of the obstructions susceptible to operation