We have investigated the effects of CP-96,345 and SR-48968, new nonpeptide (neurokinin) NK1 and NK2 receptor antagonists, respectively, against bronchoconstriction and airway microvascular leakage induced by inhaled sodium metabisulfite (MBS) in anesthetized guinea pigs. Lung resistance (RL) was measured for 6 min after challenge, followed by measurement of extravasation of Evans blue dye into airway tissues, used as an index of airway microvascular leakage. MBS (80 mM, 30 breaths) caused a significant increase in RL and leakage of dye at all airway levels. CP-96,345 (2 mg/kg, intravenous) but not SR-48968 (1.5 mg/kg, intravenous) significantly inhibited the leakage of dye at all airway levels except for trachea. Each antagonist inhibited significantly the maximal increase in RL. The combination had a significant additive effect against the bronchoconstriction, when compared with SR-48968 alone, and significantly inhibited the leakage of dye at the same airway levels as CP-96,345. We conclude that bronchoconstriction induced by inhaled MBS is, at least partly, mediated by activation of both NK1 and NK2 receptors, and the airway microvascular leakage by NK1 receptor stimulation alone.