Twenty-two children with attention deficit-hyperactivity disorder underwent a double-blind, placebo-controlled, crossover evaluation of the efficacy of standard methylphenidate twice a day and comparable doses every morning of a sustained-release preparation of methylphenidate (SR-20 Ritalin), a sustained-release form of dextroamphetamine (Dexedrine Spansule), and pemoline. The children were participating in a summer treatment program in which they engaged in recreational and classroom activities. Dependent measures include evaluations of social behavior during group recreational activities, classroom performance, and performance on a continuous performance task. Results revealed generally equivalent and beneficial effects of all four medications. Dexedrine Spansule and pemoline tended to produce the most consistent effects and were recommended for 10 of the 15 children who were responders to medication. The continuous performance task results showed that all four medications had an effect within 2 hours of ingestion, and the effects lasted for 9 hours. The implications of these results for the use of long-acting stimulant medication in children with attention deficit-hyperactivity disorder are discussed.