Predictors of response to methylphenidate (MPH) among 47 children with ADHD and mental retardation (MR) were studied at the University of Pittsburgh School of Medicine, and the Western Psychiatric Institute and Clinic, Pittsburgh, PA. A double-blind, placebo-controlled evaluation of two doses of MPH (0.3 and 0.6 mg/kg), using Conners Scales, with data collected on weekday and Saturday laboratory classrooms, showed that: 1) higher parent ratings of impulsivity and activity level at baseline were associated with greater gains in weekday classroom dependent measures; 2) higher weekday teacher measures of activity level, impulsivity, inattention, and conduct problems at baseline were related to improvement on Saturday laboratory classroom dependent measures; and 3) male Caucasians of higher socioeconomic status were more likely to show clinical improvements than other subjects. Race and conduct problems had predictive utility specific to children with MR. 
COMMENT. The higher the level of hyperactivity and associated inattention in children with ADHD and MR, the greater the beneficial response to methylphenidate. Similar findings have been reported previously in a study of 30 children of normal IQ with ADDH, using actometer measurements of motor activity and a neuropsychological test battery, and also in animals with hyperactivity induced by prefrontal cortical lesions. (Ped Neur Briefs Oct 1987; June 1991).
Children with ADD without hyperactivity or moderate levels of abnormality on Conners Scales are less likely to benefit from stimulant medication than those with ADD and H. Baseline measures of behavior by Conners Scales in ADDH children with MR were more predictive of medication response than the measures obtained in the laboratory classroom.