Complete study of patients with symptoms and signs of cerebrovascular ischemia requires adequate evaluation of the intracranial as well as the extracranial vessels. This can be accomplished safely and rapidly by performing aortic arch injections of contrast medium and filming the cerebral and extracerebral vessels. The key to producing a high yield examination is the supplemental procedure of routine Light Intensity Variation Subtraction of all of the key films, in all the angiographic series.