Twenty-three Dermatophagoides pteronyssinus (Dpt)-sensitive asthmatic children aged 7–14 years entered a double-blind, placebo-controlled trial of standardized immunotherapy (IT) (Alpare) while resident at high altitude. Dpt sensitivity was evaluated by skin prick tests at different allergen concentrations at the enrollment and after 6 and 12 months of treatment. Bronchial hyperreactivity was evaluated at the same time points, and on each occasion, histamine challenge and, the following day, Dpt bronchial challenge were performed. All patients, irrespective of active treatment, improved clinically and in lung function with increased PC20 and Dpt-PD20. Alpare-treated patients had a significantly decreased sensitivity on Dpt skin testing (P ≤0.009) and felt that their asthma had improved (P ≤0.001) compared with placebo-treated subjects, but there was no difference between the treatment groups in lung function or bronchial challenge response. IT neither increased nor decreased bronchial histamine sensitivity. Our results indicate that Dpt IT benefits asthmatic children, but improvement by allergen avoidance at high altitude is even greater.