The effects of methylphenidate (MPH) and sodium valproate (VPA) on the visual event related potentials (VERP) and EEG of children with ADHD were evaluated at the Department of Psychology, Tel Aviv University, Israel, and North Shore University Hospital, Cornell Univ Med College, New York. Two subgroups of ADHD were identified: one with abnormal and the other with normal EEGs and VERPs. The amplitude of the ERP slow negative wave was reduced by MPH and VPA in the abnormal group but was unaffected in the group with normal VERPs. 
COMMENT. The effect of medications in ADHD children appears to be related to electrophysiological findings. A positive effect is expected in patients with abnormal EEGs and VERPs.