The principal objective of this study is to determine the effect of ethanol on the metabolism of neurosteroids in the central nervous system. Neurosteroids such as 5a-pregnane-3a-ol-20-one (5a,3a-THP or Allopregnanolone) and 5a-pregnane-3a,21-diol-20- one (THDOC) have been shown to modulate the GABA/benzodiazepine binding sites and to exert anxiolytic and hypnotic effects. Modulation of these neurosteroids in the central nervous system by ethanol may be one of the underlying mechanisms for stress- related situations often observed in human alcoholics during withdrawal. In the past year, we have established a mass spectrometric technique which has adequate sensitivity to routinely measure trace levels of neurosteroids in cerebrospinal fluid(CSF). Specifically, GC/MS was used after derivatizing neurosteroids with an electron capturing moiety. Using this approach, we were able to detect pregnenolone, 5a,3a-, 5b,3a-, 5a,3b-THP, androsterone, testosterone, dihydrotestosterone and dihydroepandrosterone from human and monkey CSF samples. We found that human and monkey CSF contain both 5a,3a- and 5a,3b- THP at 5-170 picogram/ml concentrations while 5b,3a-THP is present at a concentration less than 5 pg/mL.