The primary objective of the study is to assess whether chronic treatment with olanzapine over a five-month period produces a significant increase in abnormalities in glucose levels. The main secondary objective is to evaluate whether the increase in glucose levels and rate of glucose abnormalities differs between Olanzapine and Risperidone during this treatment period. Additional secondary objectives of the study are to investigate similar questions with respect to glycohemoglobin, triglycerides and other measures of glucose and lipid metabolism.