We examined relationships in normal volunteers between cerebrospinal fluid (CSF) concentrations of the serotonin metabolite 5-hydroxyindoleacetic acid (5HIAA) and scores on the Hostility and Direction of Hostility Questionnaire. There was a significant negative correlation between CSF 5HIAA levels and scores on the "urge to act out hostility" subscale, as well as a similar nonsignificant trend with CSF levels of homovanillic acid. These results suggest that among normal individuals reduced central serotonergic tone may be associated with impaired impulse control.