Extra-intercranial arterial vascular anastomosing is a surgical form of treatment in selected patients with ischemic cerebral diseases. For the demarkation of the indication for an operation and for the objectification of the functional results cerebrovascular radionuclide angiography was carried out in seven patients with cerebrovascular insufficiency before and after the bypass operation. The non-invasive method only requires an intravenous bolar radionuclide application. It permits a well reproducible appraisal of the regional cerebral blood flow. The best functional results of the shunt operation were observed in the radionuclide angiogram of patients with pronounced focal perfusion reductions. Functionally unsatisfactory results were obtained with low-degree diffuse perfusion reductions of one hemisphere. The results permit to derive criteria for the surgical indication.