During the last two years 17 patients of the ENT-Department of the University of Heidelberg suffering from squamous-cell carcinomas of the head and neck underwent a balloon occlusion test of the internal carotid artery (ICA). The investigation was performed because of tumorous infiltration of the large cervical vessels. The balloon occlusion of the ICA was accomplished at the Department of Neuroradiology of the University of Heidelberg. While stopping bloodflow in the ICA of one side for 15-20 min, clinical, electrophysiological and Doppler sonographic monitoring was performed, to detect severe cerebral complications. The specific electrophysiological monitoring contained the detection of MSSEP's (median nerve stimulated somatosensorial evoked potentials) and TCMEP's (transcortical motor evoked potentials) during test occlusion. Balloon occlusion was not possible in three patients because of severe arteriosclerosis. Test occlusion had to be discontinued in three patients because of clinical complications (temporary amaurosis, orthostatic complications). Finally, seven patients showed contraindications during test occlusion for permanent occlusion of the ICA. Four patients had a permanent occlusion of the ICA after tumour resection. In two patients the ICA was removed without problems in test occlusion. The third patient underwent a permanent carotid occlusion because of bleeding complications (in spite of poor clinical tolerance of the test occlusion). In the fourth patient, only intraoperative neuromonitoring with MSSEP's was conducted before permanent carotid occlusion. All four patients did not show any neurological deficits after resection of the ICA. Neurophysiological monitoring played an important role in predicting cerebral complications after permanent occlusion of the ICA.