This paper reviews the evidence for various biological mechanisms in autism and discusses implications of these mechanisms for treatment. A brief introductory discussion examines the history of research on autism. Then the literature is reviewed and treatment implications are drawn for the following biological mechanisms: genetic disorders; biochemical factors; birth injury; and structural abnormalities. The paper concludes that the evidence strongly supports the probability of multiple causation for the autism syndrome. Studies designed across diagnostic categories with a developmental perspective are encouraged. The limited clinical applicability of existing biological information is recognized, and practitioners are encouraged to continue to individualize intervention based on information about a particular child. The correction of the erroneous psychodynamic explanation basing autism on parental pathology is seen as the most important improvement in the treatment of autistic children. The effectiveness of structured instruction and the importance of teaching spontaneous communication are stressed. Includes 12 references. (DB)