The NOAK study (optimization of anti-inflammatory asthma treatment using exhaled nitric oxide to improve asthma-related quality of life within primary health care) was a randomized, controlled trial on F E NO-guided treatment with asthma-related quality of life and asthma symptom control as endpoints. Details on sampling procedure and **data** collection have been described elsewhere. 38 A brief description of methodological procedures is given here. Informed written consent was obtained prior to the start of the study from all participants. The study was registered in clinical trials, NCT00421018, and was approved by the regional ethics committee in Stockholm (Dnr: 2006/185-31). A sample of 181 patients with asthma (87 women, 94 men) aged 18-64 years were recruited at 17 primary health care centres in seven different county councils in central and southern Sweden from November 2006 to March 2010. All participants had a diagnosis of asthma and had confirmed IgE sensitization to at least one airborne perennial allergen. The participants were non-smokers since at least 1 year before inclusion. Included patients had a previous smoking history of maximum 10 pack-years.