Recent studies suggest that granulocytes (PMNs) play a role in the pathogenesis of acute and chronic myocardial ischemia and extension of myocardial injury. Granulocytes can release a variety of molecules mediating tissue injury which act synergistically with other molecules and cells. The aim of our investigation was to evaluate the granulocyte function in patients affected by coronary artery disease (CAD) and during coronary angioplasty (PTCA). We studied 20 patients suffering from CAD. The PMN's aggregating activity was greater in the coronary sinus than in the aorta (P<0.01). The increase in aggregating activity was evident in patients who were smokers: their cells release significantly lower quantities of leukotriene C4 (P<0.025). In the 20 patients who underwent coronary angioplasty we analyzed superoxide release after stimulation with phorbolmyristate‐acetate (PMA). The results showed a greater decrease of PMN's superoxide production in the coronary sinus than in the aorta (P<0.05). In all patients affected by CAD we evaluated the PMN's expression of CD11b/CD18 membrane integrins. In these patients the increase in expression of CD11b/CD18 was statistically significant in comparison with the controls (P<0.01). This increase in expression correlates with a higher aggregation (r=0.87, P<0.001). The potential role of leukocytes, oxygen radicals, leukotrienes and granulocyte enzymes in the pathophysiology of myocardial injury due to regional ischemia and reperfusion is an area of intense investigation. This paper presents studies carried out in vivo which have been instrumental in demonstrating the role of granulocytes as mediators of myocardial ischemia.