Seven patients with narcolepsy-cataplexy were continuously monitored during the day using polygraphy and videotape recording. The patients were free to do whatever they wanted while confined to a sitting-at-a-table situation. Daytime activity was evaluated by distinguishing between two polygraphically defined states, namely active wakefulness and quiet wakefulness. The data from the patients were compared with those from 7 normal subjects who were studied under the same experimental conditions. While all patients had recurrent daytime sleep episodes, none of the controls napped during the recording period. The narcoleptic patients showed an altered structure of wakefulness: they spent more of their time awake in the state of active wakefulness and less in quiet wakefulness than the control subjects. Moreover, the patients remained in the quiet state for shorter periods. Daytime sleep selectively diminished the state of quiet wakefulness, whereas it did not affect the amount of time spent in active wakefulness. In addition, in 3 patients there was a clear-cut alternation of periods of sustained wakefulness and transitional phases with a mixture of sleep and wakefulness which occurred rather regularly, suggesting an ultradian cycle of sleepiness.