Lumbar CSF HVA [homovanillic acid] and 5-HIAA [5-hydroxyindoleacetic acid] levels were assayed in 3 groups each of 10 subjects, which were, respectively, deprived of sleep for 30 h, deprived of REM [rapid eye movement] sleep and disturbed with several awakenings during SW [slow wave] sleep for 2 consecutive nights. HVA levels after total sleep (39 .+-. 20 ng/ml) or REM (35 .+-. 11 ng/ml) deprivation and after SW sleep awakenings (32 .+-. 26 ng/ml) did not differ 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 [5-hydroxytryptamine] turnover after REM deprivation and possible 5-HT role in REM sleep regulation in humans were discussed.