The C-C chemokine eotaxin is thought to be important in the selective recruitment of eosinophils to the site of inflammation in guinea pigs, mice, and humans. We isolated the rat eotaxin gene to determine whether a similar molecule might play a role in the pulmonary infiltration of eosinophils during acute inflammation in the rat. The cDNA for rat eotaxin encoded a 97-amino acid protein containing a 74-amino acid mature eotaxin protein with 97.3% identity to mouse eotaxin. The recombinant protein encoded by this gene displayed specific chemotactic activity for eosinophils when analyzed with a microchemotactic chamber. The expression of eotaxin mRNA increased approximately 1.6-fold immediately after exposure to ozone and was 4-fold higher after 20 h. The number of lavageable eosinophils at the same time points were 3- and 15-fold greater, respectively, than control eosinophils. Immunocytochemistry revealed that alveolar macrophages and bronchial epithelial cells were positive for eotaxin. These results suggest that eotaxin may be involved in the recruitment of eosinophils into the air spaces during certain inflammatory conditions in rats.