The clinical response to three dose levels of methylphenidate (5, 10, and 15 mg BID) in 23 children with ADD+H and 17 children with ADD-H is reported from the Department of Psychiatry, University of Massachusetts Medical Center, Worcester, MA. Both groups of children with ADD showed significant improvements in behavior, inattention, self-control, and academic performance. A low dose was as effective as the moderate or high doses in changing the behavior at school but moderate to high doses were needed to produce improved behavior at home and better task performance on the clinic assessment battery. The greatest effect of medication on the ADD-H group occurred at the low dose. In contrast, the drug effect for the ADD+H group was linear, improving with each dose increase. In subsequent clinical recommendations drug treatment was prescribed more often in the hyperactive group (71% of children) than in those without hyperactivity (24%). Children with ADD+H were rated as having more pervasive behavioral problems than the children with ADD-H. Children with ADD+H were impaired in behavioral inhibition and vigilance whereas children with ADD-H were more impaired in the retrieval of verbally learned material. [1]