It is controversial whether the mucociliary transport system in the nasal mucosa of persons with allergic rhinitis is upregulated after an allergen challenge in vivo. The aim of this study was to assess the effect of a specific allergen challenge on the mucociliary transport system in allergic rhinitis. We used a challenge of house dust mites or a control substance on one side of the nose of 97 volunteers (54 with allergic rhinitis for house dust mites and 43 without allergies). The mucociliary transport system of the ipsilateral or contralateral side of the nose challenged was evaluated using the saccharin clearance time on the right side of the nose. The saccharin clearance time was significantly shortened after an allergen challenge not only on the ipsilateral (right) side of the nose (from 15.0 +/- 11.6 to 10. 9 +/- 9.2 min, mean +/- SD, p = 0.041) but also on the contralateral (left) side of the nose (from 14.7 +/- 10.1 to 8.1 +/- 7.9 min, p = 0.013) in the allergic group. A reduction of the saccharin clearance time was also seen in the allergic group after a control challenge [ipsilateral (right) challenge: from 13.0 +/- 10.0 to 11.6 +/- 10.6 min, contralateral (left) challenge: from 13.5 +/- 9.0 to 10.2 +/- 10.1 min]. There were no reductions of the saccharin clearance time after an allergen or control challenge in the nonallergic groups. These results suggest that a unilateral nasal challenge accelerates the mucociliary transport system bilaterally in the nose of subjects with a hypersensitivity such as allergic rhinitis.