In Macaca sylvana restrained in chairs, continuous 24 h recordings were obtained of scalp EEG, neck EMG, bilateral EOG, motility of the head and lever manipulation. A total of 32 days were studied in 8 monkeys. Recordings were divided into epochs of 30 sec and analyzed in a PDP-12 computer. Four stages of sleep and 5 stages of wakefulness were identified by combination of the above data. Results were as follows: (1) During the night, there was 21% wakefulness and during the day 20% sleep, including a considerable amount of REM. (2) Recordings of spontaneous motility of head and hands proved an excellent indicator of sleep-wakefulness cycles. (3) Spectral analysis revealed the cyclic characteristics of non-REM sleep, with peaks at 360, 149, 72, and 55 min. (4) Stages of wakefulness had ultradian cycles, and stage W-2 was the most important in number and duration of occurrences. (5) Night wakefulness had characteristics different from day wakefulness. (6) Study of sequences showed that stage II was the least differentiated being transitional among the other stages, while stage III-IV was never preceded by wakefulness or REM, and almost always it followed stage II (99.0% of the time). (7) The high statistical significance of results obtained under restraint in different monkeys suggests that this situation has great potential value in the investigation of physiological mechanisms of ultradian rhythms.