 The primary goal of this trial is to compare the efficacy and safety of COMBIVENT CFC MDI with albuterol HFA MDI, the current standard reliever medication in asthma. In the first cross-over part of the study Treatment Phases 1 and 2 the marketed product, COMBIVENT CFC MDI will be used. In the second, parallel group part of the trial Treatment Phase 3 COMBIVENT RESPIMAT will be tested for acute bronchodilator efficacy in a blinded manner at the clinic visits. During the third 4-week treatment phase open label COMBIVENT RESPIMAT will be used for symptom relief as needed. 