Changes in sleep after eastward flight; To go to bed at 2300 hr in SFO, which corresponds to 1600 hr in TYO, means that a traveller from TYO starts his sleep from evening nap in TYO. In evening naps, Slow Wave Sleep(SWS) is increased and REM sleep is decreased. In the flight from West to East, however, the subjects experienced one night total sleep deprivation. Consequently, it is necessary to do research on naps after total sleep deprivation. REM sleep is clearly increased in the morning and decreased in the evening in spite of one night total sleep deprivation. These findings indicate that the distribution of REM sleep is not affected by total sleep deprivation, but REM sleep has a clear circadian rhythm. By contrast, SWS is increased in the morning, afternoon and evening naps after total sleep deprivation. Thus, SWS is more independent of circadian effects and responsive to the length of prior wakefulness. From the findings mentioned above, it is assumed that the decrease of REM sleep and the increase of SWS in the first part of the sleep in SFO may be caused by effects of one night total sleep deprivation and circadian rhythm of REM sleep. Changes in sleep after westward flight; The sleep after returning home from east and after the flight from TYO to LDN was different from that in baseline nights in TYO, with decreased REM sleep latency, appearance of SOREMs and increased REM sleep. Since the sleep after westward flight corresponds to that in the early morning to forenoon in the place before the flight, it is necessary to investigate the effect of sleep reversal and naps in daytime. In naps after one night total sleep deprivation, morning naps had shortened REM sleep latency, increased REM sleep and frequent SOREMs. From the findings mentioned above, it is suggested that the nocturnal sleep after returning home from east and in LDN may reflect the circadian rhythm of sleep in the place before the start of the flight.