The study addresses the effect of an acute (2 hour) exposure of ozone at 0.4 ppm on the inflammatory response in the upper airways of 10 normal volunteers and compared these results to those obtained in the lower airways assessed by bronchoalveolar lavage (BAL). The results indicate significant increases in the number of polymorphonuclear neutrophils (PMN) in NAL immediately post exposure (7.7-fold). This increase is still detectable 18 hours post exposure (6-fold) which is similar to the increase of PMN in BAL. The albumin level, which is an indicator of epithelial cell permeability, was elevated 18 hours post exposure (1.5 fold). Interestingly, several other markers of acute inflammation such as prostaglandin E2 (PGEalpha), C3a, urokinase-type plasminogen activator (U-PA), which were found to be significantly elevated in the BAL of the same group of subjects (18 hours post exposure), were not elevated in the NAL either immediately post or 18 hours post exposure. Collectively the data suggest that NAL may serve as a sensitive and reliable technique to detect inflammation in the upper airways of subjects exposed to ozone.