An increasing body of evidence suggests that Group A beta-Hemolytic Streptococcal throat infections (GABHS) may trigger the onset of obsessive-compulsive disorder (OCD) and/or tic disorder in certain vulnerable children via an autoimmune process. In this subgroup of children with childhood-onset OCD and tic disorders, preliminary data suggest some children have a rapid response to amoxicillin. After only 24 to 48 hours of treatment, they have a dramatic reduction in OC symptoms and tics. To date, we have observed this phenomenon in at least 5 children, each of whom relapsed when the amoxicillin was stopped. These observations raise a number of questions, including whether or not amoxicillin has a direct central nervous system (CNS) effect or an indirect effect through perturbations of the immune system (e.g., cytokine shifts).