The purpose of this study is to determine whether nocturnal environmental control with Temperature controlled Laminar Airflow (TLA) is effective as add on treatment in patients with perennial allergic asthma.

Exposure to inhaled allergens is a pathogenetic factor in allergic asthma. However, physical, chemical and combined methods aiming to reduce airborne allergen levels have shown little or no effect in reducing asthma symptoms in people who are sensitive to perennial allergens.Aims and objectives: This study aims to investigate treatment with Temperature controled Laminar Airflow (TLA) with a very low particle concentration directed to the breathing zone in subjects with allergic asthma during night sleep. The hypothesis is that the decreased allergen exposure during the night will have an effect on quality of life and bronchial inflammation.

Method: This is a multicentre, double blind, randomized 52 week parallel trial comparing active TLA treatment with Placebo. For ethical reasons the randomization is 2 to 1 for active and placebo treatment, respectively. A 2 weeks run-in period is inserted between inclusion and randomization, during which the patient shall get familiar with the use of the patient asthma diary and to adhere to the requirements of the study participation. First 12 weeks an unchanged maintenance medication will be kept and week 13-52 medication will be modified to obtain asthma control according to international guidelines (GINA). After inclusion, run-in, randomization and baseline measurements active/placebo treatment with AA will be implemented over 52 weeks.

Inclusion Criteria:

• Consent to participate voluntarily. Willing and able to comply with the study specific procedures. Signed Informed Consent prior to any study procedure.
• Perennial allergic asthma, male and female, age 7 through 70 years, at time of randomization.
• A miniAQLQ/PAQLQ score of ≤ 5.5.
• Sensitive to pet allergen and/or house dust mites as demonstrated by changed to RAST 0.70 or positive skin prick test (wheal reaction similar to histamine control).
• Daily maintenance dose of at least ICS ≥200µg/day of budesonide or ≥100µg/day of fluticasone since at least 6 months
• Features of partly controlled asthma according to GINA

Exclusion Criteria:

• Current smoker (Non-smoker is defined as abstinent since > 1 year). Children: Parents'indoor smoking.
• Participation in another allergen avoidance program
• Participation in drug trial the preceding 3 months
• Multiple chemical sensitivity (e.g. paint, petrol, perfumes) as primary etiology
• Allergen injection or sublingual treatment in the preceding 2 years
• ICS ≥1200µg/day of budesonide or 1000µg/day of fluticasone
• Significant cardiovascular disease
• Participation in the present trial of a family member within the same household

Other protocol-defined exclusion criteria may apply