Summary The recently reported observation that the sleep state activates the appearanceof epileptiform abnormalities in the electroencephalogram are confirmed and extended. Furthermore it is shown that the use of mildly sedative doses of Nembutal to promote sleep in children does not significantly reduce the activating properties of this state. The routine use of sedative-induced sleep is shown to be a valuable adjunctto routine clinical electroencephalography in children for the following reasons: 1. Latent epileptiform activity not present in a waking record and not activated by such measures as hyperventilation may nevertheless become manifest during sleep. 2. A primary convulsogenic focus may be revealed in sleep when the wakingrecord is of a type suggestive of a generalized convulsive state. 3. Sleep produced by mild sedation provides a means of obtaining diagnostictracings in children in whom, because of mental retardation, physical handicap, or behavioral difficulties, it would not otherwise be possible. The characteristics of the various clearly abnormal electrical dischargeswhich occur during sleep are described and discussed in relation to their clinical correlates.