The effect of the xanthine oxidase inhibitor allopurinol and the non-steroidal antiinflammatory agent azapropazone on infarct size in rats, subjected to 48 h of occlusion of the left anterior descending coronary artery, were studied. Allopurinol (50 mg/kg i.p., twice daily from 24 h before to 48 h after LAD occlusion) and azapropazone (100 mg/kg i.p twice daily from 24 h before to 48 h after LAD occlusion) significantly reduced infarct size when compared to saline-treated rats. These data point towards involvement of xanthine oxidase derived free radicals in evolving myocardial infarction in rats; beneficial effect of azapropazone in this model may be related to the drug's ability to inhibit xanthine oxidase as well as various key neutrophil functions.