SUMMARY. Introduction: Exercise capacity is reduced in many patients with bronchiectasis, but there is little information available regarding exercise responses in these patients. Objectives: The aim of this study was to investigate exercise capacity and exercise responses in patients with bilateral bronchiectasis in order to identify possible exercise-limiting factors. Population and Methods: Fifteen patients with bronchiectasis aged 50±16 years underwent lung function testing, including assessment of tidal expiratory flow limitation (EFL), and performed a maximum incremental (20 watts/min) symptom-limited bicycle exercise test. Results: Exercise performance was reduced in 7 of the 15 patients, particularly in those with a greater degree of impairment of lung function, and specifically lower FEV1 (p<0.001) and FVC (p<0.001). EFL was detected in 5 of the 7 patients with exercise limitation and absent in all with normal exercise capacity. Patients with reduced exercise capacity exhibited significantly lower maximal ventilation (V.Emax %pred; p<0.001), maximal tidal volume (VTmax; p= 0.03), breathing reserve (higher V.Emax/MVV; p<0.001), peak-exercise oxygen saturation measured by pulse oximetry (SpO2, p<0.001), O2-pulse (p<0.001) and anaerobic threshold (AT, p<0.001) and perceived a higher degree of dyspnoea (Borg score; p=0.007). The best correlate of maximal work rate (WRmax, %pred) was the AT (r= 0.90, r2 = 0.81, p<0.001), while for peak oxygen uptake (V.O2max, %pred) the most significant correlation was the peak-exercise SpO2 (r=0.83, r2 = 0.69, p<0.001). Conclusions: Patients with bronchiectasis who have tidal EFL and a low FEV1 exhibit a reduction in exercise capacity. Ventilatory limitation, desaturation and impaired O2-transport/utilization to the periphery appear to be the principal factors limiting exercise. V.O2max can be predicted accurately from parameters obtained by simple means, such as peak-exercise SpO2 obtained by pulse oximetry. Pneumon 2009, 22(4):306-314.