Many neuropathological studies in autism have reported a reduction in numbers of cells in the brain in areas which control motor coordination and cognitive functioning. While the mechanism of this loss in cell number is unknown, a recent study demonstrated the presence of inflammation in the same brain areas. This suggests that an autoimmune process may play a role in the neuronal loss observed in autism. Autoimmunity occurs when the immune system not only protects the body against infectious microorganisms, but mounts an immune response against one's own tissue. This experiment will investigate whether the mechanisms which regulate autoimmunity are inadequate in children with autism and whether this is accompanied by signs of immune system activation. Measures of immune function will also be coupled with diagnostic instruments to shed light on whether changes in immune system activation is related to the severity of autism symptoms which is different from individual to individual. Significance: Determining the precise role of specific immune activity may elucidate an important immune mechanism leading to inflammation in CNS of autistic patients, as well as open new therapeutic possibilities for these patients.