Comparison of effects of ondansetron and meperidine on postanesthesia shivering treatment is the goal of this study. inclusion criteria are ASA I,II patients with postanesthesia shivering after laparatomic surgeries, no respons to surface warming , shivering score more than 1 . Exclusion criteria are age less than 20 and more than 60 years old,hepatic disease,drug alergic reactions,history of prolonged QT syndrom in relatives, history of pulmonary disease, convulsion,alergy to narcotics, consumption of Tricyclic Antidepressants or Monoamine oxidase inhibitors , elevated Intracranial Pressure , sever renal disease, hypothiroidism,narcotic drug addiction. Population of study is the patients with postanesthesia shivering in recovery room of firoozgar hospital. Total sample size is 40 and the trial is double blinded. Drug intervention is injection of 8 milligram ondansetron intravenously or 25 milligram meperidine intravenously in recovery room to control postoperative shivering. Final aim of the study is to define the success rate of ondansetron in treatment of shivering and comparison of the time to end shivering between 2 drugs.