HYPERKINESIS is a poorly understood but common disorder of childhood the main features of which are excessive motor activity, a short span of attention, low tolerance of frustration and hyperexcitability, often resulting in learning difficulties and a poor motor performance even where intelligence is normal. The neurophysiological substrate of this disorder remains undefined and emotional factors have often been invoked as its sole basis. Some children with this syndrome improve when given central nervous system stimulant drugs; We have attempted to distinguish those children who are likely to improve from those who may not.