Regional cerebral blood flow may be compromised during aneurysm surgery. This may occur during vessel occlusion by temporary clips or result from malposition of the definitive aneurysm clip. Post-operative cerebral vasospasm may also compromise cerebral blood flow and is an important cause of morbidity. This study addresses the need for a sensitive indicator of compromised cerebral function during aneurysm surgery by measuring brain tissue oxygenation and laser Doppler flow. Four patients were studied, all of whom had ruptured middle cerebral artery aneurysms. Brain tissue oxygenation measurements were made with a closed polarographic sensor placed in the ipsilateral cerebral hemisphere to the aneurysm. A laser Doppler flow probe and intracranial pressure monitor were similarly placed. The data were simultaneously processed using multimodality recording monitoring. The monitoring was continued during the post-operative period and totalled over 190 hours. Data were analysed as specific events and as trends. Initial tissue oxygen levels were low but improved in all cases as the intracranial pressure was reduced. This effect was independent of the cerebral perfusion pressure. Laser Doppler flow provided an indicator of compromised brain function and tissue oxygenation an indicator of established ischemia.