This project is designed to provide additional support for the hypothesis that abnormal maternal autoantibodies may be one cause of autism. The study will build on preliminary results in rhesus monkeys that tested prenatal exposure to immunoglobulin G (IgG) class antibodies against human fetal brain tissue. This study will expand the number of test subjects and also increase the time period of antibody exposure into the second trimester on some subjects. The monkeys will then be followed for at least two years, evaluating behavioral development and performing longitudinal magnetic resonance imaging (MRI) scans. If maternal autoantibodies are identified as a risk factor for autism, this finding would quickly lead both to the development of a diagnostic assay for maternal autoantibodies and to the development of therapeutic interventions to diminish this autism risk factor.