Article abstract—Lumbar cerebrospinal fluid levels of homovanillic acid and 5-hydroxyindoleacetic acid, the major metabolites of dopamine and serotonin, respectively, in hyperactive children did not differ significantly from those of age-matched controls. Dextroamphetamine treatment substantially reduced the spinal fluid content of homovanillic acid but not of 5-hydroxyindoleacetic acid. No change in levels of either monoamine metabolite occurred with placebo therapy. In hyperactive children receiving dextroamphetamine, the amount of homovanillic acid decline correlated closely with the degree of clinical improvement. These results support the view that an alteration in central dopamine-mediated synaptic function may occur in children manifesting the hyperactive syndrome.