Bronchial hyperresponsiveness (BHR) is regarded as a hallmark of asthma, yet it is also present in a considerable number of chronic obstructive pulmonary disease (COPD) patients. Epidemiological studies have shown that BHR provides complementary information to forced expiratory volume in 1 s (FEV(1)) for development and progression of COPD. We hypothesised that the severity of BHR and its longitudinal changes associate with both clinical and airway inflammation measures in COPD. Our hypothesis was tested in 114 COPD patients (median age 62.9 years, smoking exposure 45.9 pack-yrs) participating in the GLUCOLD (Groningen Leiden Universities Corticosteroids in Obstructive Lung Disease) study, which previously showed an improvement in BHR with fluticasone and fluticasone/salmeterol. At baseline, and 6 and 30 months after treatment, we investigated lung function, including body plethysmography, provocative concentration of methacholine causing a 20% fall in FEV(1), sputum induction, and bronchial biopsies. By performing both cross-sectional and longitudinal analyses, we show that BHR in COPD is predominantly associated with residual volume/total lung capacity (a measure of air trapping) and airway inflammation reflected by the number of neutrophils, macrophages and lymphocytes in sputum and bronchial biopsies. Our findings indicate that BHR is an independent trait in COPD and provides important information on phenotype heterogeneity and disease activity.