The mast cell serine protease tryptase has been implicated as a critical mediator of airway hyperresponsiveness in vitro and in vivo. We have previously demonstrated that tryptase promotes hyperresponsiveness in isolated guinea pig bronchi. In this study, we have investigated the potential role of tryptase-mediated activation of proteinase-activated receptor-2 (PAR-2) in promoting airway hyperresponsiveness. Ex vivo exposure of guinea pig bronchi to the PAR-2 agonists H₂N-Ser-Leu-Ile-Gly-Arg-Leu-CONH₂ (SLIGRL) and t-cinnamoyl-H₂N-Leu-Ile-Gly-Arg-Leu-O-CONH₂ (t-c-LIGRLO) (0.1–10μM) induced a concentration-dependent increase of contractile response to histamine. Treatment with 10μM SLIGRL or t-c LIGRLO for 45min increased subsequent responsiveness to histamine (0.3mM) by 54±3% and 69±5%, respectively (P<0.05 vs. control). In contrast, the PAR-1 agonist peptide H₂N-Ser-Phe-Leu-Leu-Arg-Asn-CONH₂ (SFLLRN) did not promote significant changes in the airway. Effects of the peptides were observed following at least a 30-min preincubation with the tissue. Coincubation with indomethacin or removal of epithelial cells is required for PAR-2-mediated hyperreactivity. The inactive analogue H₂N-Leu-Ser-Ile-Gly-Arg-Leu-CONH₂ (LISGRL; 10μM) failed to promote hyperresponsiveness. Neuropeptide antagonists blocked the effect of the PAR-2 agonists. Selective antagonists of NK1 (L-703,606), NK2 (L-659,877), and CGRP (αCGRP 8–37) provided additive inhibition of PAR-2-mediated hyperreactivity. Pretreatment of bronchi with capsaicin (0.8μM) also prevented the effects of SLIGRL. These results demonstrate the potential involvement of tryptase-mediated activation of PAR-2 in promoting airway hyperresponsiveness. These results further demonstrate that the PAR-2-mediated response involves a neurogenic mechanism involving neuropeptide release.