Wysocki H, Minczykowski A, Wykretowicz A, Juniczak G; Smielecki J. Medical Academy, Poland. Arch Immunol Ther Exp (Warsz) 1995;43(3-4):187-90 Peripheral polymorphonuclear neutrophils (PMN) number, percent of PMN bearing IgG Fc receptors as well as PMN adherence were evaluated in 29 patients submitted to an exercise test. The peripheral PMN count significantly increased at the maximal work load. The increase in number of neutrophils bearing IgG Fc receptors was also noticed at that point, while PMN adherence to nylon wool columns did not change significantly. Nine subjects were additionally submitted to diagnostic transesophageal atrial pacing with a rate similar to maximal heart rate observed during the exercise test. It was revealed that atrial pacing in these patients had no influence on the peripheral PMN count, PMN adherence as well as number of neutrophils bearing IgG Fc receptors. We conclude, that granulocytosis observed during exercise can not be solely attributed to the increased heart rate and increased cardiac output but other mechanisms like muscle work play a significant role in this process.