Introduction: Asthma is a chronic respiratory disorder primarily driven by increased airway inflammation. It is one of the most prevalent chronic conditions affecting Canadians. It is the most common chronic illness affecting children and the fourth most common disorders affecting adults. In 2001, nearly 2.2 million (8.4%) Canadians were diagnosed as having asthma. More importantly, asthma is an escalating medical problem in Canada, e.g., between 1994 and 2001, there was a 40% increase in the number of Canadians with asthma. Not only is the prevalence of asthma increasing, but there has been a rapid rise in the morbidity and costs associated with asthma and its poor control. The WHO estimated that the global cost of caring for asthma exceeds that of AIDS/HIV and tuberculosis combined. Though recent guidelines have emphasized the importance of improving asthma control and quality of life, leading to huge amounts of resource being dedicated to this, more than 50% of adult patients with asthma remain poorly controlled. As current treatment strategies appear to be failing, it is important to target simple, cost effective interventions that are applicable for most patients with asthma and will increase overall levels of control and decrease asthma morbidity. There is evidence to suggest that aerobic exercise may improve asthma symptoms and control in children. In addition, there is evidence that exercise directly improves inflammatory and immune profiles in non-asthma patients, which may provide the mechanism by which exercise could improve asthma. However, there are no known studies that have systematically assessed the effects of aerobic exercise on asthma control, quality of life or immune function in adult asthma populations.