A total of 229 subjects were investigated between October 1999 and June 2004: 130 patients with AE-COPD, 65 patients with stable COPD and 34 smokers without COPD. The clinical characteristics and lung function measurements are summarized in table 1. FEV 1 , FEV 1 in % of predicted value and FEV 1 /FVC were normal in smokers, significantly decreased in stable COPD patients (all) and further significantly decreased in AE-COPD patients (all p < 0.05 compared to stable COPD and all p < 0.001 compared to smokers).