Near infrared spectroscopy (NIRS) is a non invasive, portable, safe technique for monitoring cerebral oxygenation and haemodynamics. Since it does not involve the use of ionising radiation it may be used repeatedly to produce serial measurements of CBF and CBV in patients, and continuously to provide trend data about cerebral circulation changes. NIRS allows measurements to be made at the bedside with minimal disturbance to other monitoring and treatment procedures. Although regional information is not yet available, good time resolution allows rapid changes in cerebral haemodynamics to be observed.