Twenty-seven patients with allergy to house-dust mite and the clinical symptoms of perennial rhinitis and/or mild asthma were treated with specific immunotherapy (SIT) with standardized extracts of house-dust mite for 3 years. The success of therapy was evaluated in yearly intervals by 1) subjective rhinitis and asthma scores. 2) allergen-specific skin and conjunctival tests. 3) nonspecific bronchial hyperreactivity to methacholine. 4) medication scores of rhinitis and asthma. SIT induced a significant improvement of all parameters already after 1 year, with further improvement in the follow-up measurements at 2 and 3 years. We found a constant improvement of the rhinitis and asthma symptom scores, a reduced reactivity in the skin prick and conjunctival provocation tests, and a constantly increasing reduction of bronchial hyperreactivity to methacholine. Concomitantly, the use of medication (topical corticosteroids, beta2-mimetics, and antihistamines) was reduced. Our data support the concept that SIT with standardized extracts of house-dust mite results in an improvement of allergen-specific parameters in patients with perennial rhinitis and intermittent asthma. This beneficial effect of SIT on allergen-specific immune parameters seems to induce also a diminution of nonspecific bronchial hyperreactivity and enables reduction of symptomatic treatment.