Macrolides such as erythromycin have been shown to have potent anti-inflammatory effects in in vitro experiments and in other lung conditions such as cystic fibrosis and bronchiectasis as well as in open label studies in COPD. We hypothesised that long term therapy with oral erythromycin would reduce airway inflammation and reduce the frequency of exacerbations in patients with COPD. If these properties are demonstrated this therapy can have potentially important benefits if effective in this condition.