The purpose of this investigation was to study neutrophil (PMN) aggregation in the aorta and coronary sinus of 20 patients with angiographically documented coronary artery disease (group I) compared with eight patients with normal coronary arteries (group II). PMNs were separated from the other blood components and their aggregation response to Ca2+ ionophore A 23187 l x 10(-5) M (final concentration) was measured. Group I patients had higher aggregating activity in the coronary sinus than in the aorta (24.9 +/- 3.7 vs 18.7 +/- 3.4 average maximum delta T, P less than 0.01), while no difference was found in group II (coronary sinus 16.7 +/- 3.5; aorta 16.3 +/- 2.4 average maximum delta T P = NS). Among group I patients, smokers had a significantly higher aggregating activity than non-smokers, whereas no correlation was found between aggregation response and blood cholesterol values. These data suggest that the presence of atherosclerotic plaques in coronary vessels may prime PMNs so that they show greater aggregating response to subsequent stimulation.