Individuals with Asperger’s disorder and high functioning autism often don’t have diagnosis during the childhood because of their high intelligence. It is not easy to diagnose adults as pervasive developmental disorder, because the information about their state and episodes in the childhood depends on the retrospective memories by caregivers and themselves. Although some researchers proposed that biological indicators might be useful for diagnosis,they have not found reliable indicators yet. Diagnosis of pervasive developmental disorder based only on biological indicators has limitations,because pervasive developmental disorder is biologically heterogeneous, and the diagnosis criteria were made based on abnormal behaviors,but not on the biological characteristics. However it is expected that the biological indicators that are useful to diagnose will be found in the near future. The outlines of neuroimaging and eye tracking studies that are relatively simple and useful methods, including findings of our studies, are introduced in this review.