Urinary catecholamine excretion was assessed in 15 boys with attention-deficit/hyperactivity disorder (ADHD) and 16 normal controls during a defined physical and mental task. Dihydroxyphenylalanine, dopamine, norepinephrine (NE), epinephrine (EPI), 3,4-dihydroxyphenylacetic acid, and 3,4-dihydroxyphenylglycol (DOPEG) concentrations were assayed by high-pressure liquid chromatography with electrochemical detection. The urinary concentration of DOPEG, an NE metabolite that has not been previously measured in ADHD, was significantly lower in the ADHD subjects than in the normal controls. There was also a trend for lower urinary EPI levels in the hyperactive boys. Stepwise multiple regression analyses demonstrated that DOPEG and EPI each contributed significantly to the variance in the behavioral symptoms within the full sample. The results are consistent with previous reports of abnormal metabolism of norepinephrine and epinephrine in ADHD. These neurochemical findings may be due to differences between ADHD and normal boys in neuronal (central or peripheral) or nonneuronal (e.g., adrenal, renal) activity. The results are also consistent with prior findings in normal children of an inverse relationship between EPI excretion and inattentive, restless behaviors. Together, these findings suggest caution in ascribing metabolite changes to ADHD or to ADHD-like behaviors that may be seen in normal children.