The value of the EEG has not been diminished by the advent of new diagnostic procedures and the improvement of older techniques. For electro-encephalography is in essence a 'clinical' method, reflecting in its own particular way, the variable status of the brain. Moreover, in conjunction with these methods the EEG can provide for better information concerning the brain's condition. Furthermore in particular serio-angiography and C.B.F. measurements can furnish us more detailed insight in the EEG phenomena which may occur in differed types of cerebro-vascular disease. Generally the changes of the local EEG phenomena, which may occur in cerebral ischaemia correlate well with the angiographic and r.C.B.F. data. In cerebral haemorrhage and cerebral tumour however the r.C.B.F. values are commonly more diffusely reduced as could be expected from the extent of the EEG disturbances. Increased r.C.B.F. values may be encountered over meningioma due to increased perfusion of the Xenon133 in this electrically inactive tumour; they can also occur in malign glioblastoma, where direct arterio-venous connections are responsable for the so called shunt peaks. These peaks may also be found in patients with arterio-venous malformations or with acute ischaemia, in the latter case due to marked reduction of the local pH. Remarkable was the discrepancy between the local increase of the C.B.F. and the local deterioration in the EEG following intracarotid injection of HC1 papaverine; the same applied to the reaction of EEG and C.B.F. in case of acute induced hypertension with loss of autoregulation.