A subclinical EEG seizure occurred in each of 2 patients during a test that repeatedly evoked probable mild cerebral hypoxia. The firing rate of the neurons was unaffected until the EEG seizure had been ongoing for over a minute. After the EEG seizures, all neurons were profoundly depressed regardless of whether their responses to hypoxia had been an increase, decrease, or no change in firing rate. These observations indicate that the mechanism responsible for post-EEG seizure depression of neuronal firing is probably not cerebral hypoxia.