The effects of methylphenidate on a number of objective measures of activity level and attention were assessed on three repeated occasions in four types of settings: free play, movie viewing, testing, and restricted play periods. Subjects were 36 boys between 5 and 12 years of age and of average intelligence. Of these, 18 were diagnosed as hyperkinetic and participated in a double-blind drug-placebo crossover design. The remaining 18 boys, matched in age and IQ with the hyperkinetic children, served as a control group and received no drugs. Results indicated that compared to placebo, methylphenidate significantly reduced wrist, ankle, locomotor, and seat movement activity in the hyperkinetic children regardless of the type of setting in which the measures were taken. Relatively fewer significant drug effects were noted on the measures of concentration or attention. While concentration to reaction time, maze performance, and a movie viewing task improved during drug treatment, the length of attention to toys in free play was not significantly improved. Parental ratings of activity level were also improved by the drug. The hyperkinetic children were also observed to increase their level of task-irrelevant activity over time while control children remained relatively stable in activity over repeated assessment. Despite the positive drug effects, clinical observations suggested that methylphenidate may have reduced the interest of some children in their environment.