Patients with schizophrenia and Tourette's disorder will be compared to normal controls with respect to the uptake of the dopamine neurotransmitter-dependent tracer 6-18F-DOPA by positron emission tomography (PET). PET allows quantification and localization of tissue radionuclide content with high spatial resolution. 6-18F-DOPA, an analogue of L-DOPA allows in vivo visualization of dopamine and its metabolites in the areas of the brain believed to be involved in schizophrenia and Tourette's disorder.