In the present work, on the basis of an unselected collection of patients suspected of epilepsy, the diagnostic value of waking and sleep recordings each after 24 h sleep deprivation are compared with one another. Indicative findings of epilepsy were found in 16.7 % of the cases in the waking EEG after sleep deprivation. In the sleep EEG after sleep deprivation this amounted to 57.1 %. These figures speak for the advantage of the second method. The result is highly significant with a x2 value of 13.01 (p < 0.01).