Biological studies on autism have become popular from the 1970s, and theories founded upon some forms of dysfunction of the CNS are coming to be accepted world wide. However, despite the voluminous studies undertaken to present, the biological markers of the disorder are as yet unknown, and there are many problems remaining in the present state wherein we are dependent upon diagnoses made on the behavior level. The behavior characteristics of autism and the problems in extracting its early signs, methods of evaluating behavior changes in pharmacotherapy and determination of its safety were discussed.