We measured changes in basal release of nitric oxide (NO) and its effect on polymorphonuclear neutrophil (PMN) adherence to endothelial cells (EC) in a feline model of myocardial ischemia and reperfusion (MI/R). Significant reductions in basal NO release occurred 10 minutes following reperfusion, whereas increases in PMN adherence occurred at 20 minutes post-reperfusion. Addition of hSOD blocked the post-reperfusion adherence of PMNs to the endothelium. These results indicate that decreased basal release of NO, following MI/R precedes enhanced PMN adherence to the coronary endothelium, which may lead to PMN-induced myocardial injury.