In a randomized, double-blind study the effects of the standard form of methylphenidate (10 mg given twice daily) were compared to those of a sustained-release form of methylphenidate (20 mg given once daily) in outpatient children with minimal brain dysfunction. The study was 2 weeks in duration and involved 30 children. Psychometric tests completed by the children, as well as physician, teacher and parent questionnaires were used to measure drug effects. Comparisons between the 2 methylphenidate treatment groups showed no consistent significant changes which could be deemed clinically favorable for one group over the other nor were there significant improvements over pretreatment measurements for either group. Adverse reactions--headache, hyperactivity, restlessness were reported by 5 patients receiving the sustained-release and 2 receiving the standard methylphenidate.