 Patients with COPD experience exacerbations that are a major cause of morbidity. Exacerbations are associated with increased airway and systemic inflammation and those experiencing frequent exacerbations demonstrate increased inflammation in the stable state. Tiotropium has been shown to reduce exacerbation frequency and it might be postulated that this is due to a reduction in inflammation. The study will compare airway inflammation and exacerbation frequency in patients with COPD on tiotropium or placebo. 