Magnetic resonance spectroscopy, a noninvasive neuroimaging method, is a technique with the potential to measure in vivo neurochemical changes to different medication treatments. Symptoms of attention deficit hyperactivity disorder (ADHD) improved in two children treated with methylphenidate and two children treated with atomoxetine, for whom pre- and posttreatment proton magnetic resonance spectroscopy examinations were obtained to assess the relation between the neurochemical profiles in the striatum and prefrontal cortex among symptom severity and response to treatment. In the striatum, a striking decrease in the glutamate/creatine ratio (mean change 56.1%) was observed between 14 and 18 weeks of therapy in all four children with ADHD. In the prefrontal cortex, however, changes in the glutamate/creatine ratio were noted only in subjects receiving atomoxetine, not in those receiving methylphenidate. These data suggest that in vivo magnetic resonance spectroscopy measurement has the potential to assess response to psychopharmacological treatment in children with ADHD.