['Exercise intolerance is a hallmark of chronic obstructive pulmonary disease (COPD) and forced expiratory volume in one second (FEV1) is the traditional metric used to define the severity of COPD. However, there is dissociation between FEV1 and exercise capacity in a large proportion of subjects with COPD. The aim of this study was to investigate whether other lung function parameters have an additive, predictive value for exercise capacity and whether this differs according to the COPD stage.', 'Spirometry, body plethysmography and diffusing capacity for carbon monoxide (DLCO) were performed on 88 patients with COPD GOLD stages II-IV. Exercise capacity (EC) was determined in all subjects by symptom-limited, incremental cycle ergometer testing.', 'Significant relationships were found between EC and the majority of lung function parameters. DLCO, FEV1 and inspiratory capacity (IC) were found to be the best predictors of EC in a stepwise regression analysis explaining 72% of EC. These lung function parameters explained 76% of EC in GOLD II, 72% in GOLD III and 40% in GOLD IV. DLCO alone was the best predictor of exercise capacity in all GOLD stages.'] Is impaired carbon monoxide diffusing capacity the strongest predictor of exercise intolerance in COPD?