Lumbar CSF HVA and 5-HIAA levels were assayed in 3 groups each of 10 subjects, which were respectively deprived of sleep for 30 h, deprived of REM sleep and disturbed with several awakenings during SW sleep for two consecutive nights. HVA levels after total sleep (39 +/- 20 ng/ml) or REM (35 +/- 11 ng/ml) deprivation as well as after SW sleep awakenings (32 +/- 26 ng/ml) were not different from controls (42 +/- 14 ng/ml). 5-HIAA levels after REM deprivation (32 +/- 15 ng/ml) appeared increased when compared with controls (21 +/- 7 ng/ml), total sleep-deprived subjects (21 +/- 10 ng/ml) or subjects with SW sleep awakenings (27 +/- 13 ng/ml). Possible increase in 5-HT turnover after REM deprivation and possible 5-HT role in REM sleep regulation in humans are discussed.