A high incidence of infections predominantly of the upper and lower respiratory tract have been observed for years after strenuous exercise. The mucosal surfaces represent a first-line-of-defense for airborne pathogens, but little is known about their function during exercise. The purpose of this study was thus to assess the influence of long-distance running on polymorphonuclear neutrophils (PMNs) phagocytic function of the upper respiratory tract. The number of PMNs recovered by nasal lavage (NAL) was determined, and the percentage of phagocytizing PMNs and number of phagocytized E. coli per PMN was measured utilizing a fluorescence activated cell sorter. A 20 km race resulted in a 2.0-fold higher count of PMNs in the nasal lavage fluid of 12 male amateur runners (aged 34 +/- 11.3 years) immediately after the competition and a 1.6-fold higher count 1 day after the race in comparison to the pre-race value. During training (7 and 3 days before the race) and after 3 days of recreation (3 days after the race) the runners' counts were lower than immediately after the race. The percentage of phagocytizing PMNs was significantly reduced during the pre-race period, but the reduction was most striking immediately and 1 day after the race (48.7 +/- 6.4% and 54.5 +/- 6.2%). The number of bacteria ingested by the athletes' phagozytizing PMNs was 3.2 +/- 0.3 E. coli/PMN immediately after the race and 5.2 +/- 0.3 1 day after the competition. The findings suggest chronic upper airway inflammation and impaired phagocyte function after strenuous exercise. This might contribute to the observed high incidence of respiratory tract infections among participants in sports.