The aim of the study is to compare the efficacy of ciclesonide versus fluticasone propionate on lung function, time to first asthma exacerbation, asthma symptoms, use of rescue medication, and quality of life in patients with mild to moderate asthma. Ciclesonide will be inhaled at one dose level once daily; fluticasone propionate will be inhaled at one dose level twice daily. The study duration consists of a baseline period (2 to 4 weeks) and a treatment period (24 weeks). The study will provide further data on safety and tolerability of ciclesonide.