The primary diagnostic procedure for Attention-Deficit/Hyperactivity Disorder (ADHD) is the clinical interview, because psychological, neuropsychological, and neurological tests to dare have not had sufficient specificity: Currently there is no objective means to measure severity of ADHD, or the extent to which it is benefited by various dosages of medication. We recently reported that a certain EEG profile, the Consistency Index, occurring during the transition between hco easy cognitive tasks clearly differentiated ADHD from non-ADHD boys between the ages of 8 and 12. The current study replicated this with older males (19-25) using different tasks, and a double blind, placebo versus Ritalin(R) controlled crossover design. Seven ADHD subjects were found to have a significantly lower Consistency Index than 6 non-ADHD males while transitioning from 2 Simple tasks during placebo condition, while only the ADHD subjects demonstrated a significant improvement in their Consistency Index while on Ritalin(R). Similar but nonsignificant trends Mere observed while transitioning across Hard tasks.