Method: Sera from 12 patients with Tourette's syndrome with high levels of antineural or antinuclear antibodies were in- fused bilaterally into the ventrolateral striatum of rats. Sera from 12 additional Tourette's syndrome patients and 12 nor- mal subjects (both groups with low levels of autoantibodies) were infused for comparison. Rates of oral stereotypies were recorded by observers who were blind to the origin of the in- fused sera. Results: Oral stereotypies significantly increased in the rats in- fused with sera from the patients with high levels of autoanti- bodies. Conclusions: The results are consistent with an autoimmune etiology in a subset of cases of Tourette's syndrome.