To investigate the basis for widely separate rates in the diagnosis of childhood hyperactivity between the U.S. and U.K., research teams and clinician panels in both countries completed diagnostic ratings of standardized case histories using DSM III and ICD 9 diagnostic schemes. The results showed effects of diagnostic schemes on rates for the diagnosis of hyperactivity. However, there was additional effect of nationality of case, with U.S. cases more likely to receive the diagnosis of Attention Deficit Disorder. To pursue this, a new study is started comparing 24 hour motor activity in hyperactive children and their parents in three settings: Bethesda, Maryland; Irvine, California; and London, England.