In an attempt to avoid pulmonary oxygen toxicity from developing in patients whose ventilation is being continuously assisted with positive-pressure cycled ventilators, the ventilators may be driven by compressed air from a centralized compressor. The following case illustrates a potentially disastrous complication which can occur with the misuse of this system. Report of a Case A 54-year-old quadriplegic white man had his ventilation assisted, or controlled, as needed by means of a rocking bed, a Thompson pneumobelt, and a pressure cycled ventilator which was powered by compressed air from a wall outlet. While the patient's ventilation was being controlled with the pressure cycled ventilator, his wife reported that he was less responsive than usual and kept wanting to go to sleep. About two hours later, a nurse found him to be completely unresponsive, and she was unable to obtain a blood pressure reading or to palpate his pulse clearly. She