Participants in this study will undergo psychological tests, blood and urine tests, electroencephalogram (EEG), electrocardiogram (EKG), and magnetic resonance imaging (MRI) scans of the brain for the first 1 to 2 weeks of the study while taking their regular medications. Participants will then be tapered off their medications over 1 to 3 weeks and will continue to stay off medications for an additional 2 days to 3 weeks. During this time, participants will undergo psychiatric, neurological, and cardiac examinations as well as blood tests. After this period without medications, participants will be randomly assigned to receive either clozapine or olanzapine for 8 weeks. An EEG will be performed prior to treatment and after 6 weeks of study medication. Participants who respond well to the study drugs may continue to receive them through their own physician. Participants who do not respond to either clozapine or olanzapine or cannot tolerate their side effects will be treated individually with other drugs until optimum treatment is identified. Regular telephone updates and in person visits to NIH for repeat testing and MRIs will be conducted.