The effects of commonly prescribed psychotropic drugs such as methylphenidate and dextroamphetamine on the learning and school performance of children from about 5 to 12 years of age who display hyperactivity, impulsivity, and are diagnosed as MBD (minimal brain dysfunction) will be systematically studied. A number of measures will be used to assess drug effects: teacher, parent and physician rating scales; picture recognition test of short- term memory; heart rate and blood pressure under mild exercise stress; height and weight; gas chromotograph and mass spectrometry analysis of metabolities in the blood and urine; and psychological testing. An anterospective long-term follow-up will be continued on children who have received medication, of children whose medication has been discontinued, and of cohort groups. Studies of dose-response relationships between mg/kg doses of psychotropic drugs and short-term memory performance and psychophysiological measures of attention will be conducted. Based upon promising pilot data, continued research on the relationship between level of methylphenidate metabolities in the blood and urine and clinical classification as a responder or nonresponder will be conducted.