To further investigate the possible function of the serotonergic system in the pathophysiology of attention deficit hyperactivity disorder (ADHD), platelet serotonin 5-HT2A receptors were characterized for 19 ADHD children and 17 age-matched control subjects. Subjects were evaluated using the Diagnostic Interview for Children and Adolescents (DICA-R-C)-DSM IV and the Children's Depression Inventory. An aggressive subgroup was also determined by the presence of two or more positive aggressive symptoms on either subjects' or parents' reports. Platelets were isolated from venous blood and 5-HT2A receptor number, and affinity was determined using 125I-LSD binding. There was no difference in platelet 5-HT2A receptor binding characteristics between the two groups. The results from this pilot study suggest a limited function of 5-HT2A receptors in the pathophysiology of ADHD and extend the findings of other previous negative studies of the peripheral serotonergic system in ADHD.