Evidence suggests that maternal autoantibodies directed against fetal brain tissue are a possible cause for a subset of autism cases. A characteristic pattern of autoantibody production to human fetal brain tissue (and to rhesus monkey brain tissue) in 20% of mothers of multiple children with autism was recently identified. These studies indicate that rhesus monkeys, prenatally exposed to IgG class antibodies from these mothers, produce whole body motor stereotypies indicative of autism symptoms. Research on this immunological model of autism will be extended in this study by increasing the number of experimental subjects and increasing the duration of IgG exposure into the second trimester for a subset of the subjects. Behavioral observations of the first two years of development will be made in both treated and untreated animals to compare behavior in a variety of social contexts designed to probe attachments, social dominance, social motivations, and fear reactions. A detailed longitudinal magnetic resonance imaging (MRI) study of the brain regions most commonly implicated in the neuropathology of autism will also be carried out in order to evaluate differences in the time course of brain development. Collectively, these studies may have direct implications for diagnosis, prevention, and treatment of ASD.