To compare the effects of the stimulant drugs dextroamphetamine and methylphenidate on urinary and plasma monoamines and metabolites within the same clinical sample, thirty-one children with attention-deficit disorder with hyperactivity were treated with dextroamphetamine (up to 1.5 mg/kg/day), methylphenidate (up to 3.0 mg/kg/day), and placebo in an 11-week double-blind crossover trial. As expected, both drugs showed striking clinical efficacy, and within a subsample of the group, earlier findings were confirmed, that dextroamphetamine but not methylphenidate lowered urinary and plasma 3-methoxy-4-hydroxyphenylglycol and whole body norepinephrine turnover, and that urinary and plasma concentration of homovanillic acid was unaltered by either drug. Methylphenidate but not dextroamphetamine increased plasma norepinephrine. Urinary epinephrine and metanephrine were increased with both drugs, but this increase did not correlate significantly with clinical improvement.