Growing evidence obtained from human genomic analysis and antigen-challenged transgenic mice suggests that interleukin-9 (IL-9) is a candidate factor in immunoglobulin E (IgE) production and thus is thought to be associated with bronchial inflammation and bronchial hyperresponsiveness (BHR). To evaluate the expression of the IL-9 receptor and its effect on the IL-9 human bronchial cell line BEAS-2B cells, reverse transcriptase-polymerase chain reaction (RT-PCR), immunohistochemical investigation, and chemotaxis assay were performed. The components of the IL-9 receptor, consisting of IL-9 receptor alpha (CD129) and IL-2 receptory ((1)132), were expressed on BEAS-2B cells as determined by RT-PCR and flow cytometry. BEAS-2B cells exposed to IL-9 released neutrophil chemotactic activity (NCA) in a time- and dose-dependent manner, and the presence of granulocyte colony-stimulating factor (G-CSF) was also detected. This factor is primarily involved in NCA for the measurement of cytokines and in the inhibition assay of neutrophil chemotaxis. These findings suggest that bronchial epithelial cells may express IL-9 receptors, and that IL-9 may induce airway inflammation through the release of G-CSF from bronchial epithelial cells.