Routine and awake EEGs following 24-hour sleep deprivation were studied in 119 patients with closed head injury, 64 epileptics without any history of head injury and 53 healthy controls. The results were compared to CT brain scan findings. There were no epileptic discharges in routine EEGs, while EEGs after 24-hour sleep deprivation showed considerable activation, ranging from 28 to 37.5% in those with a history of head injury or epilepsy. No correlation was found between the period elapsed between the time of injury and the activation of the EEG. Most of the patients with EEG activation after sleep deprivation had abnormal CT scans. EEGs following 24-hour sleep deprivation therefore appear to be a useful adjunct to other methods used in detecting brain damage in patients with head injury or epilepsy.