At each study visit the peak expiratory flow (PEF) diary will be retained and spirometry performed. Patients will record morning and evening PEF measurements and daily symptoms throughout the study. Airway responsiveness to methacholine, asthma control score, asthma quality of life questionnaire, induced sputum, exhaled NO and blood samples for immunological tests, lipids and liver functions will be performed at visits 5, 6 and 9. Pregnancy tests will be performed in all women of child-bearing age at visits 2 and 6 and subjects will be informed about adequate contraception during and for one month after the study.