It became evident in two patients during cerebral angiography that ligation of an internal carotid artery would probably be necessary in the course of a subsequent neurosurgical operation. A balloon catheter was inserted and the internal carotid artery was occluded. A continous EEG recording was made with a Fourier transformed frequency analysis before and during the occlusion; the motor functions of the corresponding side of the body were observed simultaneously on the conscious patient. EEG alterations indicative of cerebral ischemia were not demonstrated in either patient during an occlusion period of 7 min. Unilateral neurosurgical ligation of the common carotid artery and the internal carotid artery was performed on one patient. As predicted no neurological deficit occurred.
