The aim of this study is to assess and compare efficacy and safety of BI 54903 at doses of very low dose twice daily (b.i.d) and low dose once daily (evening dosing) and placebo over an 12-week treatment period in asthmatic patients aged 12 to 65 years inadequately controlled on short acting beta-2 agonist (SABA) therapy alone as demonstrated by a decrease in forced expiratory volume in 1 second (FEV1) (not less than 10 %, and equal to or less than 25%) and an Asthma Control Questionnaire (ACQ-6) of not less than 1.5 at time of randomisation.