(Background) For protection of the brain, hypothermia is a helpful therapeutic approach in patients who remain comatose after return of spontaneous circulation (ROSC). The 2010 CPR Guidelines recommend that extracorporeal cardiopulmonary resuscitation (ECPR) using an emergency cardiopulmonary bypass (CPB) should be considered for patients with cardiac arrest. However, it is not yet clear whether this therapy can improve cerebral circulation and oxygenation in these patients. To clarify this issue, we evaluated change of cerebral blood oxygenation (CBO) during ECPR using near-infrared spectroscopy (NIRS). (Methods) Between November 2009 and June 2011, we employed NIRS (NIRO-200NX, Hamamatsu Photonics, Japan) to measure CBO in the bilateral frontal lobe in patients transported to the ER after out-of-hospital cardiac arrest. Enrollment criteria were: aged 18-74 years; cardiac arrest witnessed by bystanders; presumed cardiac etiology of cardiac arrest according to the Utstein style guidelines; estimated time interval from collapse to paramedic’s arrival at patient’s side within 15 min; defibrillation using automated external defibrillator by bystander and/or emergency medical personnel; and persistent cardiac arrest on arrival at the ER. (Results) Fifteen patients met the above criteria. The tissue oxygenation index (TOI) on arrival at the ER was 36.5%. This increased to 67.8% during ECPR (P<0.001). The patients whose TOI subsequently decreased had a favourable neurological outcome (figure). (Conclusion) The increase of TOI during ECPR might reflect an improvement in cerebral blood flow, while the decrease of TOI after ECPR might reflect oxygen utilization of the brain tissue as a result of neuronal cell survival. NIRS may be useful for monitoring cerebral hemodynamics and oxygen metabolism during CPR.