This study showed that nasal allergy patients have increased nasal airway resistance and tissue kallikrein activity in nasal lavage in accordance with the severity of symptoms. Nasal airway resistance and tissue kallikrein activity were significantly increased in the nasal lavage collected 15 min after antigen challenge, placement of a disk containing house dust antigen. The free kinin level in the nasal lavage collected 15 min after the antigen challenge was also markedly increased. Pretreatment of patients with d-chlor-pheniramine maleate (histamine H1 receptor antagonist) blunted this increase in nasal airway resistance and tissue kallikrein activity 15 min after the antigen challenge, suggesting that histamine may accelerate excretion of tissue kallikrein in nasal secretions. Camostat mesilate inhibited the in vitro tissue kallikrein activity in nasal lavage collected from allergy patients. Administration of camostat mesilate significantly inhibited nasal airway resistance and tissue kallikrein activity in nasal lavage after the antigen challenge, indicating that kinin generated in the nasal cavity increased nasal airway resistance. These results suggest that tissue kallikrein inhibitors may serve as anti-allergic drugs by suppressing the nasal symptoms of nasal allergy patients.