The purpose of this study is to answer the question whether a disease-specific profile of breath in patients with asthma can be detected by an untargeted metabolomic study using exhaled breath analysis by mass spectrometry.

Inclusion Criteria:

1. Confirmed asthma. Diagnosis of asthma is made with episodic chest symptoms and a documented reversibility of at least 12% and/or 200 ml in FEV1 after 200 ug of inhaled salbutamol or airway hyperresponsiveness in the case of normal lung function testing (PC20 methacholine < 4mg/ml) at the time of diagnosis.
2. Age between 18 and 80 years at study entry.
3. Healthy controls: never-smokers, normal spirometry (baseline FEV1 > 85% predicted and FEV1/FVC greater than 0.7).

Exclusion Criteria:

1. Asthma exacerbation within the last 6 weeks, defined as worsening of asthma symptoms requiring a change in therapy by a physician or a change in regular asthma therapy (including short course of oral corticosteroids)
2. Any lung disease other than asthma.
3. Acute inflammatory disease (e.g. common cold) within the last 4 weeks.
4. Regular intake of oral steroids.
5. Active smoking habits / positive history of smoking.
6. Acute or chronic hepatic disease.
7. Renal failure or renal replacement therapy.
8. Pregnancy.

Patients suffering from asthma will be included according to the predefined inclusion and exclusion criteria.

Healthy controls will be recruited from the general population by printed flyers, newspaper advertisements and personal communication.