During the past year, our research has continued its investigation of central nervous system (CNS) serotonin correlates of low CSF 5-HIAA and tolerance to the intoxicating effects of alcohol. To assess the role of impaired serotonin functioning and intrinsic tolerance on excessive alcohol consumption and the related high levels of aggression, CSF was obtained from alcohol naive rhesus macaque subjects and assayed for CSF 5-HIAA concentrations. Subjects were then dispensed identical doses of IV alcohol and rated for levels of intoxication. Following the ratings for intoxication, subjects' were allowed to consume an alcohol solution. (1) Subjects with lower ratings for intoxication and low CSF 5-HIAA were more likely to consume alcohol to excess. (2) Peer-reared monkeys (monkeys reared without adults, with only age-mates present), were also more likely to consume alcohol to excess. (3) Rates of aggression measured while the subjects were intoxicated were correlated with lifetime rates of severe aggression, suggesting that high rates of aggression during intoxication are an extension of a lifelong pattern of severe aggression, rather than a special form of aggression. (4) As an extension of these findings, interindividual differences in CSF 5-HIAA concentrations were also shown to correlate with time to recover from ketamine anesthesia. (5) Subjects with low CSF 5-HIAA concentrations also showed high serotonin transporter binding, as measured by beta-CIT uptake in SPECT imaging. High beta-CIT uptake was correlated with high rates of aggression and minimal intoxication following a modest dose of alcohol. (6) Studies were initiated that investigated neuroanatomical differences in frontal serotonin functioning in monkeys with low or high CSF 5-HIAA concentrations. (7) PET studies continued to investigate the underlying serotonin synthesis rates in subjects with low and high CSF 5-HIAA concentrations.