By the criteria for the determination of brain deathe established in The Korean Medical Association, an appneic patient's PaCO2 must be greater than 50 torr before apnea can be attributed to brain death. Blood gases were analized in 35cases of brain death by the conventional criteria. The data of PaCO2, pH, PaCO2 in the apnea test of the cases were erratic, but a PaCO2 had increased 50 torr in each patient esaily. To perform the apnea test satisfactorily, it is essential to keep oxygen catheter deep into the tracheal tube by at least 10cm for adequate appneic oxygenation, and indwelling arterial catheters were available for rapid, timed blood sampling. And to determine the accuracy of blood gas measurements, duplicate samples drawn less than 4seconds apart were sent to clinical lagoratory in each test. The apneic test is a crucial rapid and safe performance for the determination of brain death. I recognize.