Repeated intranasal administration of interleukin 8 (IL-8) induces bronchial hyperresponsiveness (BHR) accompanied by lower airway neutrophil accumulation (ANA) in guinea-pigs. Leukotriene B4 (LTB4) is a chemotactic factor for neutrophils. To elucidate whether LTB4 and neutrophil elastase are involved in the IL-8-induced BHR and ANA, the effects of a LTB4 antagonist (ONO-4057) and a neutrophil elastase inhibitor (ONO-5046) on the responses were examined. IL-8 (5 microg x kg[-1]) was administered intranasally to guinea-pigs twice weekly for 3 weeks. One day after the last administration, animals were anaesthetized and artificially ventilated through tracheal cannulae, and lateral pressure at the tracheal cannula (Pao) was measured as an overall index of airway responses to inhaled histamine. ONO-4057 (2 or 20 mg x kg[-1]) or ONO-5046 (30 or 300 mg x kg[-1]) was administered intraperitoneally 24 and 1 h before anaesthesia. ONO-4057, but not ONO-5046, significantly inhibited the IL8-induced BHR and ANA, assessed by bronchoalveolar lavage, in a dose-dependent manner. These findings suggest that interleukin 8 causes bronchial hyperresponsiveness and airway neutrophil accumulation in guinea-pigs in vivo. In part this appears to be due to release of leukotriene B4, whereas it may not be mediated by neutrophil elastase.