The local EEG, the local cerebral blood flow (lCBF), and the flow in the distal stump of the occluded middle cerebral artery was simultaneously recorded in 28 acute experiments in cats. Nembutal anaesthesia was used eleven times, and Halothane anaesthesia 17 times. The recordings were made via platinum electrodes: 12 in the ischaemic hemisphere, and 2-3 in the opposite non-ischaemic hemisphere. The flow in the occluded middle cerebral artery was recorded via a platinum electrode introduced into this artery via the transorbital approach. The changes in lEEG, lCBF, and middle cerebral artery flow were studied during normotension, hypertension, and hypotension. A beneficial effect of hypertension was noted in the acute phase of brain ischaemia. Hypertension counteracted also the "diaschisis" in the non-ischaemic part of the ischaemic hemisphere and in the opposite non-ischaemic hemisphere. A correlation between lEEG changes and lCBF changes was noted. In addition, an interesting discrepancy was observed between the rapid H2 clearance in the middle cerebral artery stump and the much slower H2 clearance in the ischaemic brain area. Significant differences between experiments under Halothane and experiments under Nembutal anaesthesia were noted. In the acute phase those changes are probably the result of the different levels of blood pressure in those two groups.