The study objective is to investigate in a placebo-controlled, double-blind manner the effect of inhaled corticosteroid (ciclesonide) on airway hyperresponsiveness measured as having PD15 mannitol. Treatment medication will be administered as follows: 320 microgram ciclesonide or placebo will be inhaled once daily. The study duration consists of a treatment period of 4 weeks. The study will provide further data on safety of ciclesonide.

Inclusion Criteria:

1. Referred to the pulmonology department of the university hospital Basel because of suspected asthma defined as respiratory symptoms like wheezing or cough or chest tightness.
2. Asthma symptoms partly controlled according to GINA (October 2006) 1 week prior to randomization
3. FEV1 ≥ 70% predicted
4. 18 - 70 years old

Exclusion Criteria:

1. Smoker and ex-smoker with >10 pack years
2. COPD
3. Upper respiratory tract infection within the past 4 weeks.
4. ICS or oral steroids during the previous month before inclusion
5. b-blockers within the past 4 weeks
6. Current treatment with medication as defined in section concomitant medication (ICS other than study medication, ß-blockers)
7. Pregnancy
8. Known malignancy