A number of myths have grown up regarding the behavioral effects and use of stimulant medications with children. The first is that there is a type of child uniquely responsive to stimulant compounds, namely, the hyperkinetic child. The second is that the hyperkinetic child is any child who is sufficiently overactive to be considered a menace by adults. The third is that the stimulant medications act primarily to reduce motor activity in a paradoxical "sedative" fashion; and finally, that the drugs do not influence cognitive and perceptual functioning in these children. I believe that these myths are due partly to the historical accident of the manner in which they were first studied, partly to the imprecision in diagnosis and terminology of classification of patients, and partly to the paucity of systematic data on sufficiently large samples under sufficiently varied experimental conditions. I would like to present the results of studies which bear on these issues, and try to draw some general conclusions regarding the present state of knowledge with regard to the use of the various psychostimulants. In this paper I will deal with dextroamphetamine, methylphenidate, and magnesium pemoline. I. METHYLPHENIDATE AND DEXTROAMPHETAMINE The children for this study were referred from schools, pediatricians, and social agencies for either academic or behavioral difficulties, or both. The subjects retained for the drug study comprised about ⅔ of the original referral sample. They were selected to fit the description of the child with "minimal brain dysfunction" as defined by the National Institute of Neurological Diseases and Stroke (NINDS) Task Force I report.