Asthma is a chronic disorder of the airways primarily driven by increased airway inflammation, and is an escalating medical problem in Canada. For example, between 1994 and 2001 there was a 40% increase in the number of Canadians who had asthma. Not only is the prevalence of asthma increasing but there has been a rapid rise in the number of asthma events and costs associated with asthma and poor asthma control. It has been estimated that the global cost of caring for asthma exceeds that of AIDS/HIV and tuberculosis combined. These increases have occurred in spite of the development of clear asthma management guidelines. There is evidence to suggest that aerobic exercise, e.g., running or cycling, may improve asthma symptoms and control in children. However, there are currently no studies that have systematically assessed the effects of exercise on asthma control or symptoms in adults. The current proposed study will assess the effects of aerobic exercise in sedentary patients with poorly controlled asthma. In addition to usual medical care, 52 patients will participate in a supervised aerobic exercise program. The program will consist of 3 X 1hr sessions of supervised exercise per week for 12 weeks. Another 52 patients will only maintain usual medical care. The asthma control, quality of life, and inflammatory profile will be evaluated at baseline and following the 12 weeks of treatment. The investigators believe that: (1) The exercise intervention will significant improve asthma control and asthma quality of life; (2) The exercise intervention will result in significant improvements in inflammatory profiles; and (3) These changes in the inflammatory profile will be directly related to the improvements in asthma control and quality of life.