The response to stimulant drugs of 48 boys with attention deficit/hyperactivity disorder was measured following dextroamphetamine, methylphenidate, and placebo in a double-blind crossover study. To distinguish lack of behavioral improvement from adverse drug effects, a day hospital setting and a wide dose range were used. Both drugs were highly and equally efficacious for the group as a whole, and frequently one drug or the other was superior for an individual child, or adverse effects occurred only on one of the stimulants. Only one of the 48 boys (2%) was discharged without the recommendation for continued stimulant drug treatment. "Nonresponse" appears to be extremely rare when both stimulants and a wide range of doses are given.