The aim of this study was to determine the effects of nonsteroid antiinflammatory drugs on oxidative stress in rats subjected to laparotomy. Rats (n=50) were divided into five equal groups. Control group (n=10, Group I) received physiological saline whereas Groups II-V (n=10 in each) received metamizole (50 mg/kg), flunixin meglumine (2.5 mg/kg), carprofen (2.5 mg/kg), or diclofenac (2.5 mg/kg) by intraperitoneal injection for 5 days following the operation. On postoperative day 6, blood samples were obtained; levels of malondialdehyde (MDA) and nitric oxide (NO) in serum, and erythrocyte glutathione (GSH), catalase levels were determined. NSAIDs caused a decrease in MDA, NO and GSH levels, whereas catalase levels increased with NSAID treatment. In conclusion, NSAIDs may have additional beneficial effects to their anti-inflammatory effects by diminishing the oxidative stress.