105 men and women between the ages of 18-50 years with asthma will be randomly assigned to one of two treatment groups: exercise therapy or control. The exercise therapy protocol is detailed below. The control group will receive usual asthma care. The control group will be instructed to maintain their current sedentary activity level, i.e. not to begin a formal or informal exercise program. In order to standardize contact with study personnel between the two groups the control group will be seen three times a week for clinic visits (exercise group will have sessions three times a week). The primary outcome measures are asthma control (asthma symptom score) and asthma-related inflammation. Secondary outcomes include exacerbation rate, asthma-related quality of life, generic quality of life, lung function, airways hyper-reactivity, and cardiovascular fitness. The effect of exercise therapy on inflammatory markers in blood, and sputum will be assessed by comparing results obtained at study completion versus those obtained at baseline.