The IL-33 pathway involved in the development of type-2 airway inflammation is activated in patients with allergic asthma. According to the "one airway, one disease" concept, the IL-33 pathway should also be activated in the airways of patients suffering from allergic rhinitis. Methods We compared the levels of IL-33 and its mRNA precursor, in induced sputum of patients suffering from seasonal allergic rhinitis (n=27) with those measured in patients with seasonal allergic asthma (n=23), in atopic asymptomatic subjects (n=9), and healthy controls (n=17), in and out of the pollen season. Results Medians IL-33 levels were higher in sputum supernatants of allergic rhinitis (9.4 pg.ml-1) and asthma patients (5.2 pg.ml-1) when compared to controls (0 pg.ml-1; p<0.001) or to atopic asymptomatic subjects (0 pg.ml-1; p=0.006). The same was observed with qPCR. IL-33 levels were similar in and out of pollen seasons in patients suffering from allergic rhinitis (4.9 pg.ml-1 vs 7.1 pg.ml-1, p=0.256) or allergic asthma patients (3.6 pg.ml-1 vs 3.2 pg.ml-1, p=0.61). Conclusion IL-33 is detectable in the lower airways of patients suffering from allergic rhinitis and to similar levels than in patients suffering from allergic asthma.These levels appear to be independent of atopy per se and of natural variation in allergen exposure. Those data provide evidence of a silent epithelial dysfunction in the airways of patient suffering from allergic rhinitis without asthma, further confirming the «one airway, one disease» theory linking asthma and rhinitis.