The mean etiological factors in acute exacerbations in general are thought to be viral and bacterial infections and air pollution (6). Newer molecular techniques have shown that bacterial colonisation, a common finding in patients with clinically stable COPD, is not stable, and that there is a frequent turnover of the strains of H. influenzae that illicit specific host responses to outer membrane proteins. A change in the strain, but not in the organisms, is therefore likely to be the cause of the symptoms of an exacerbation (16–18). Viral infections of the lower respiratory tract in patients with COPD can also cause direct damage to the airway epithelium resulting in loss of ciliated epithelium, increased mucus production, slowing of necrotic cells into the airway lumen, and increased plasma exudation (19). Studies with polymerase chain reaction (PCR) to detect virus m-RNA have shown viruses in nearly 30% of patients with acute, mostly muculent, exacerbations of COPD, predominately rhinoviruses (20). Air pollution has been recognised as a cause of exacerbations during the past 40 years, and there is now overwhelming evidence that the amount of air pollution, especially particulates, is associated with acute exacerbations (21, 22).