There is increasing evidence that airway epithelial cells play an active role in allergic inflammation, including bronchial asthma. We showed that human airway epithelial cells in culture release GM-CSF, G-CSF, M-CSF, IL-6, and IL-8, using a serum-free culture system. These cytokines are known to modulate the bioactivities of inflammatory cells that accumulate at the site of inflammation. Among them, GM-CSF, IL-8, or both may be important because they influence the bioactivities of eosinophils, which are characteristic of allergic inflammation. Here we report on the effects of air pollutants such as suspended particulate matter and diesel exhaust particulates on release of cytokines from airway epithelial cells. All air pollutants we tested stimulated epithelial cells to release GM-CSF. These results suggest that one cause of the recent increase in the prevalence of allergic disorders is direct stimulation of airway epithelial cells by air-pollutants. Furthermore, anti-inflammatory agents such as steroids and anti-allergic drugs were found to suppress the release of GM-CSF from airway epithelial cells in vitro.