The antiallergic drug repirinast (30 mg/kg i.p.) significantly inhibited antigen-induced early and late pulmonary responses in guinea pigs. The same dose of repirinast significantly inhibited bronchoalveolar lavage eosinophilia and neutrophilia 5 h after antigen challenge (at the peak of the late response). Histologic examination revealed that repirinast markedly inhibited leukocyte (predominantly eosinophils) infiltration into bronchial tissue. Repirinast also blocked antigen-induced airway hyperresponsiveness to inhaled acetylcholine. The inhibitory effect of repirinast on the infiltration of eosinophils and/or neutrophils into the airway may reflect the inhibition of late pulmonary response and airway hyperresponsiveness.