Plasma 3-methoxy-4-hydroxyphenylglycol (MHPG), plasma dopamine-beta-hydroxylase (DBH) activity, and platelet monoamine oxidase (MAO) were obtained in 42 boys (7-14 years old) consecutively evaluated at a community mental health clinic. The boys were diagnosed according to DSM-III criteria by a child psychiatrist using a semistructured interview with the parent and child. The Revised Behavior Problem Checklist (RBPC) and the Revised Children's Manifest Anxiety Scale (RCMAS) were consecutively obtained on the last 24 subjects. No relationship of any of the plasma measures was found with respect to the DSM-III diagnoses. Plasma MHPG was positively correlated with the parent's rating of the child's anxiety on the Anxiety-Withdrawal factor of the RBPC. Plasma MHPG as well as platelet MAO activity, correlated positively with the child's self-rating of anxiety on the RCMAS. Children classified by the RBPC as having high conduct symptoms and low anxiety symptoms had significantly lower plasma MHPG than those subjects with low conduct problems and high anxiety. Platelet MAO activity was found to be negatively correlated to the child's score on the Lie Scale of the RCMAS.