For years physicians have observed a high incidence of upper respiratory tract infections (URTI) after strenuous exercise. Mucosal surfaces represent a first-line-of-defense against infections, and pollutants or organisms entrapped in respiratory secretions are cleared by mucociliary transport. Little is known about this mechanism during exercise. The purpose of this study was to examine the nasal mucociliary clearance (MMCC) in amateur runners competing in a marathon race. Twelve amateur runners entered in an inner-city marathon race and 10 healthy sedentary subjects participated in the study. On the day of the race the outside temperature was 3 degrees C. Nasal mucociliary transit time (NMTT) was measured daily for 1 week before and 1 week after the race by the saccharin sodium/indigo carmine method. Nasal tissue biopsies were taken, and cilia beat frequency (CBF) was measured as viability and function of ciliated epithelial cells were determined. NMTT was significantly prolonged after the race (17.1 +/- 1.2 min vs 8.9 +/- 0.9 min; athletes vs control group; mean +/- SEM) and returned to baseline over several days. CBF was significantly reduced only in the first 24 hours after the race (7.31 +/- 0.65 Hz for athletes vs 9.94 +/- 0.45 Hz, controls. After the race, athletes showed a higher percentage of ciliated cells with immotile cilia (37.1 +/- 1.3% vs 27.8 +/- 1.1%, athletes vs controls) or dead ciliated cells (7.3 +/- 0.9% vs 4.1 +/- 0.8%). The findings suggest impairment of NMCC up to several days after strenuous exercise, which might be partially caused by abnormally functioning ciliated cells.(ABSTRACT TRUNCATED AT 250 WORDS)