Subjects will include 40 outpatients with schizophrenia or schizoaffective disorder treated with clozapine or olanzapine for at least one year. Twenty clozapine-treated subjects and twenty olanzapine-treated subjects with type 2 diabetes mellitus, impaired fasting glucose, or insulin resistance will be recruited. Patients will be excluded for significant medical illness, seizure disorder, substance abuse, or inability to provide informed consent.