Objectives: The authors discuss the outcomes of a study on IL-18 concentration in nasal washings after the inhalatory challenge test with flour allergens (ICHT-F) in bakers with flour-induced occupational airway allergy (OAA) Methods: We measured IL-18 concentration using ELISA kit and assessed morphological changes in nasal lavage fluid (NLF) before, and 4 h and 24 h after ICHT-F in three groups of subjects: Group A - 9 patients with diagnosed OAA (occupational asthma and rhinitis), Group B - 10 patients with atopic asthma and rhinitis, and Group C - 9 healthy volunteers. Results: In Group A, significant differences in the basophil proportion in NLF were noted only 24 h after ICHT-F. Both the basophil proportion and total eosinophil count were higher in Group A than in Group C at this time-point. Group A also showed a statistically significant increase in IL-18 levels 4 h after the challenge. A significant relationship was noted between the proportion of basophils 4 h after ICHT-F and IL-18 level at 24 h after the test. Conclusions: This is the first study demonstrating an increased expression of IL-18 in nasal washings of subjects diagnosed with OAA to flour allergens. The observed higher concentrations of IL-18 in nasal washings after ICHT as well as the increase in the proportion of basophils provide evidence for the important role of IL-18 in persistent allergic inflammation.