The first study is not yet published. We found signs of clinically significant effects of active air cleaners by the parameters ECP in serum and bronchial hyperreactivity by a cold air hyperventilation test, but the results gave p-values at the border of statistical significance, p=0.104 for FEV1 reduction, and significant results, p=0.018 for differences in the change of ECP. The number of patients included in the study was 49, a lower number than wanted in the first place. We did not find significant effects on Liz Juniper's Life Quality Scale scores. Yet, there are reasons to believe that the results of the first study may have clinical significance. A cold air hyperventilation test reflects a real life situation in interior parts of Norway, resembling outdoor winter conditions strongly. In the first study Allergy Control encasing over pillows, eiderdowns and mattresses were applied compared to placebo, but no signs of effects were found on these children aged 7 to 17 with allergy to dog or cat, but not to house dust mites. The reason to exclude house dust mite allergic patients in the first trial was to examine if encasings could have any effect on patients without house dust mite allergy, and the fact that house dust mite allergy is less common in Northern interior areas, where the trial took place. Other studies indicate, however, that air cleaners can reduce allergens from dogs and cats, but not most other indoor allergens (3). We want to perform a new trial, and publish the results from each trial in one publication, but also look upon the results of a meta-analysis of both studies. Our hope is that the two trials can give more reliable information about the effects of the air cleaners. This time, no dust analyses will be taken, because dust analyses from the first trial, sent to dr. Susanne Lau at the Charité-Virchow Clinic in Berlin, showed that the air cleaners removed considerable amounts of dust (personal message from dr. Lau). The results have been summarised in an article by Groth C et al. in Allergy in 2002, and a manuscript for an article is now sent to Allergy for publication. The efficiency of IQAir air cleaners has also been documented by Stiftung Warentest in Germany. Due to limited resources and the signs of low sensitivity in such a trial, Liz Juniper's Life Quality Scale will not be applied this time. For economic reasons, hair samples for nicotine analysis will not be taken this time.