Olanzapine was administered orally (20 mg/kg/day) in Sprague-Dawley rats. Forty-eight male Sprague-Dawley rats were divided into eight groups of six animals each. Four groups of animals received olanzapine for 7, 14, 21 and 48 days. There were no significant changes in hematological, clinical biochemistry parameters and superoxide dismutase activity in pancreas, liver and brain of all the groups. No significant changes in malonaldehyde levels were observed in liver and brain of all the groups. A significant increase in malonaldehyde levels in pancreas were observed in all the treatment groups; however, no increase in serum glucose levels were seen in these animals. A significant increase in platelet numbers in the treatment groups poses a serious threat regarding long-term use of olanzapine.