Background: Once the optimal dose is reached, subcutaneous immunotherapy [SCIT] with mite extract is capable of reducing symptoms and the need for rescue medication. Objective: To assess the capacity of a subcutaneous extract of mites [D. pteronyssinus] to bring about a reduction in concomitant medication as well as in vivo and in vitro changes in just 2-3 months of treatment in patients with allergic asthma. Methods: A total of 45 patients with persistent mildmoderate allergic asthma due to sensitisation to D. pteronyssinus were included in a multi-centre, double-blind, placebocontrolled trial. Length of treatment was 4 months. After a period for adjusting medication in order to classify asthma severity appropriately, patients were commenced on treatment of 400 or 800 μg/day of budesonide as concomitant medication. Results: After 4 months of treatment there were no significant changes in the budesonide dose between the active group and the placebo group. In the active group there was a significant difference between active and placebo group in sIgG4 [p=.0003], as well as a significant increase in the cutaneous tolerance index [2.81, CI 95%: 1.29 – 7.48, which was significant with a Confidence Interval of 95%]. These changes were not observed in the placebo group. Conclusion: After just 4 months of treatment, SCIT was capable of inducing in vivo and in vitro changes, but these changes were not reflected in improved clinical outcome within the first 4 months of therapy.