The presence of hyperoxia during reperfusion following brain ischemia has been shown in experimental animals to result in increased mortality and increased lipid peroxidation. Although no human studies have been reported, prolonged hyperoxia after resuscitation from cardiac arrest probably would result in increased cerebral injury. We report the case of an 88-year-old man who had a 5- to 6-minute cardiac arrest and then had decerebrate posturing during the post-resuscitation period, indicating that he had suffered a significant ischemic/anoxic insult. Early attention was paid to normalizing the arterial Po2 following resuscitation, which, according to experimental evidence, contributed to his eventual complete recovery of neurologic function, including mental state.