Clinical studies have shown a close relationship between variables such as hypoxia, increased intracranial pressure, arterial hypotension, or seizures and neurological outcome. This indicates the need for monitoring techniques of the central nervous system including measurements of cerebral blood flow, cerebral oxygenation and neuronal function. Semiquantitative changes in cerebral blood flow can be measured continuously using transcranial Doppler sonography. Measurements of jugular venous oxygen saturation or tissue oxygenation reflect the balance between cerebral oxygen delivery and cerebral oxygen demand. Near-infrared spectroscopy appears to be a technology with potential for non-invasive measurements of cerebral oxygen saturation and mitochondrial oxygen availability. The current technology is, however, of limited clinical utility. Brain electrical monitoring techniques such as electroencephalogram and evoked potentials are sensitive and specific to detect changes in neuronal function caused by cerebral ischaemia. Electroencephalogram and evoked potential measurements of depth of anaesthesia and specific electroencephalogram patterns for pharmacodynamic quantification of drug effects may gear the dosage of anaesthetics according to the anaesthetic effect.