The aim of this study is to evaluate the involvement of small airways in asthma, as determined by bronchial challenges, CT-scanning, and cellular markers of inflammation. Ciclesonide will be inhaled at one dose level once daily. The study duration consists of a baseline period (2 to 3 weeks) and a treatment period (5 to 6 weeks). The study will provide further data on safety and tolerability of ciclesonide.