Using a combination of an alternating treatment and double-blind placebo-controlled drug design, the independent and combined effects of two behavioral interventions and two doses of methylphenidate (MPH) in 3 children with Attention Deficit Hyperactivity Disorder (ADHD) and mental retardation (MR) were assessed. In this single subject design, 2 of the 3 subjects responded positively to medication as measured by increased on-task behavior. The first behavioral intervention, a token economy for on-task behavior, was ineffective for increasing either on-task behavior or work accuracy when combined with placebo. However, improvement in work accuracy was realized with implementation of a second behavioral intervention that specifically targeted accuracy independent of drug conditions. The current findings highlight both the positive effects and limitations of the two commonly used treatment modalities for ADHD. Future studies should continue to extend this area of investigative efforts to produce more data-based knowledge as to the appropriate doses of treatment, both pharmacological and behavioral, with children with both ADHD and mental retardation.