The effects of IFN-beta and prednisolone (Pred) on antigen-induced IgE antibody production, airway eosinophilia and airway hyperreactivity (AHR) were studied in ovalbumin-sensitized Balb/c mice. Three inhalations of antigen (ovalbumin) caused an increase in the number of eosinophils and lymphocytes in bronchoalveolar lavage fluid and AHR to acetylcholine with a significant elevation in the serum IgE level. IFN-beta clearly inhibited the antigen-induced airway inflammation and AHR, but did not affect IgE antibody production. Pred inhibited antigen-induced IgE antibody production, airway inflammation and AHR to acetylcholine. In addition, IFN-beta inhibited T-helper type 2 (Th2) cell clone (D10G4.1)-induced peritoneal eosinophilia in mice, but did not affect neutrophilia, whereas Pred inhibited D10G4.1-induced peritoneal eosinophilia and neutrophilia. These results suggest that IFN-beta inhibits antigen-induced bronchial inflammation and AHR probably due to the inhibition of Th2-induced airway eosinophilia.