Trichuris suis ova (TSO) are the eggs of intestinal helminthes which induce Th2 cytokine release and nonspecifically downregulate Th1 responsiveness (Summers et al., 2003). Treatment with TSO has been shown to have a beneficial effect in autoimmune inflammatory bowel disease (Summers et al, 2003; Summers et al., 2005a; Summers et al., 2005b) and anecdotal reports from patients with autism have demonstrated that TSO may be effective in reducing repetitive behaviors, aggression, self-injury, and impulsivity.