Neutrophils (PMNs) obtained by nasal lavage were counted to determine if ozone, an oxidant air pollutant, induces an acute inflammatory response in the upper respiratory tract (URT) of humans. Background data were obtained by the nasal lavages from 200 nonexperimentally exposed subjects. Then, using a known inflammatory agent for the URT, rhinovirus-type 39, the induction, peak, and resolution of an acute inflammatory response was shown to be documented by the nasal lavage PMN counts. To determined if ozone induces this response, 41 subjects were exposed to either filtered air or 0.5 ppm ozone for 4 hr, on 2 consecutive days. Nasal lavages were taken pre-, immediately post each exposure, and 22 hr following the last exposure. Lavage PMN counts increased significantly (p = .005) in the ozone-exposed group, with 3.5-, 6.5-, and 3.9-fold increases over the air-exposed group at the post 1, pre 2, and post 2 time points, respectively. Ozone induces an inflammatory response in the URT of humans, and nasal lavage PMN counts are useful to assay the inflammatory properties of air pollutants.