BACKGROUND The majority of allergic asthmatic patients are sensitised to several aeroallergens. Discrimination of the clinically relevant allergen is essential for the correct use of immunotherapy. OBJECTIVE To investigate nasal challenge and its role in screening clinically relevant allergens in asthmatic children. METHODS Aeroallergen nasal challenge was performed in five different groups of patients (asthma; asthma & rhinitis; rhinitis; atopic controls; and non-atopic controls). Differences between groups after challenge were evaluated by means of spirometry and acoustic rhinometry. RESULTS Nasal challenge was performed in 125 patients, 25 per group. The positive nasal response of immediate type was recorded in 21 patients with asthma only (P<0.001), 18 with asthma and rhinitis (P<0.001), 19 with rhinitis (P<0.001), two atopic control patients and in no healthy control patients. However, no differences were observed between the asthma group and the groups with rhinitis symptoms. The risk of a positive challenge was much higher in the asthma without rhinitis group compared to atopic controls (OR 29.57; 95%CI: 5.47-159.97). CONCLUSION Aeroallergen nasal challenge is a safe technique in asthmatic children and could be useful in establishing the clinically relevant allergen even in the absence of rhinitis.