Peptide leukotrienes have been suggested to play an important role in bronchial asthma. As antigen-induced bronchoconstrictions, airway hyperreactivity, and pulmonary eosinophil accumulation are characteristics of the pathology of asthma, we investigated the effect of a peptide leukotriene receptor antagonist, ONO-1078, on these responses using guinea-pig models of asthma. Oral administration of ONO-1078 (3 mg/kg) significantly inhibited slow-reacting substance of anaphylaxis-mediated bronchoconstriction induced by i.v. administered ovalbumin. ONO-1078 (30-100 mg/kg), when administered orally both 1 h before and 4 h after ovalbumin challenge, significantly reduced immediate- and late-phase asthmatic responses, with peak responses occurring immediately and 5-11 h after challenge with inhaled ovalbumin. Oral administration of ONO-1078 significantly reduced the airway hyperreactivity (10-30 mg/kg) and the pulmonary eosinophil accumulation (30-100 mg/kg) observed 4 and 24 h after ovalbumin challenge, respectively. These results suggest that ONO-1078 may be of therapeutic use for bronchial asthma.