Small airway inflammation and dysfunction will be measured in 40 children and 40 adults with asthma before and after 8 weeks of treatment with inhaled budesonide. The same measurements will be conducted once in 80 age and sex matched healthy controls.

Inclusion Criteria:

• symptoms of asthma and objective evidence of variable or reversible airway obstruction according to at least one of the following criteria
• significant response to bronchodilator (in subjects 7 years or older: FEV1 (forced expiratory volume in 1st second) or FVC (forced vital capacity) increases at least 12 % and 200 ml; in 4-6 years old subjects R5 decreases at least 40 %)
• in at least 12 years old subjects significant diurnal variation (at least 20 % and 60 l/min on at least three days) or significant response to bronchodilator ( at least 15 % and 60 l/min on at least three occasions) in PEF (peak expiratory flow) during a two-week monitoring
• significant airway hyperreactivity (PD20 FEV1 of methacholine less than 600 µg in at least 16 years old subjects, FEV1 decreases at least 15 % in exercise test in 7-15 years old, or R5 increases at least 40 % during free-running test in 4-6 years old subjects)

Exclusion Criteria:

• current smoking
• regular anti-inflammatory asthma medication (will be paused for at least 4 weeks before enrollment)
• other chronic pulmonary disease
• other diseases that in the opinion of the treating physician prevents participation