This study will include 70 patients diagnosed with schizophrenia, taking either risperidone, olanzapine or haloperidol, and 20 healthy control subjects. Each subject will undergo a 4 hour glucose tolerance test. In addition, there will be a small project within the overall study to measure the effects of risperidone and olanzapine on glucose regulation as the individuals switch from their prior treatment with a conventional antipsychotic medication to either risperidone or olanzapine. Ten subjects will be studied on a typical neuroleptic at baseline then switched over a one week period to risperidone or olanzapine. The participants will be evaluated at 1 week, 4 weeks, and 12 weeks, prospectively. Each evaluation will consist of a 4 hour glucose tolerance test.