To test the hypothesis that neutrophils contribute to acute, ozone-induced epithelial damage in the lung, rats were depleted of their circulating neutrophils by intraperitoneal injection of a rabbit anti-rat neutrophil serum (ANS) 12 hr prior to an 8-hr exposure to 1.0 ppm ozone. Additional rats were given an injection of normal rabbit serum (NRS) prior to ozone exposure. Exposures were followed by postexposure periods in filtered air for 0, 4, or 16 hr. Control rats were given either ANS or NRS and then exposed only to filtered air. Analysis of bronchoalveolar lavage fluid (BALF) from NRS-treated rats revealed a significant increase in total neutrophils above that of controls at the 4- and 16-hr postexposure times, with a peak increase at 4 hr postexposure. In contrast, there was almost total ablation of the BALF neutrophil response in the ANS-treated rats at all times. Ozone caused an increase in BALF protein, fibronectin, and interleukin-6 above those in controls in both the NRS- and ANS-treated rats, but the only significant difference between the two groups was a level of fibronectin in the neutrophil-depleted animals higher than that in the neutrophil-sufficient animals at the 0-hr postexposure time. Electron microscopic morphometry on lungs fixed by intravascular perfusion demonstrated no significant differences in the volume per surface area epithelial basal lamina (Vs) of necrotic and degenerating epithelial cells in central acini between the neutrophil-depleted and neutrophil-sufficient animals. From these results, we concluded that neutrophils do not play a detectable role in contributing to the early epithelial damage in the lung caused by an acute exposure to ozone.