The effects of theophylline on allergen-induced airway obstruction and bronchial hyperresponsiveness were investigated in allergic rabbits. This allergic rabbit model was developed in our laboratory and stimulates the human model of allergic asthma in several aspects. Four allergic rabbits with hyperreactive airways were challenged with ragweed to elicit early- and late-phase asthmatic responses and subsequent increased airway responsiveness. Two to three weeks later, the rabbits received theophylline (5 mg/ml, nebulized for 3 min) prior to a second allergen challenge. Theophylline significantly inhibited the allergen-induced early- and late-phase asthmatic responses by 38% (P < 0.05) and 49% (P < 0.05), respectively. Further theophylline inhibited the allergen-induced increase in lung resistance by 42% (P < 0.05) during the late-phase responses. Theophylline also inhibited the allergen-induced bronchial hyperresponsiveness by 39% (P < 0.05) at 24 h. These data suggest a potential anti-inflammatory effect of theophylline in preventing allergen-induced asthmatic responses and bronchial hyperresponsiveness.