The aim of this study was to assess the adequacy of oxygenation in patients with chronic obstructive pulmonary disease (COPD) on long-term oxygen therapy (LTOT) in Copenhagen county. Twenty-six patients were enrolled and assessed prospectively by 24-h pulse oximetry. Patients comprised seven males and 19 females with a mean age of 69 +/- 5 yrs, arterial oxygen tension of 6.5 +/- 0.6 kPa, forced vital capacity of 1.47 L, forced expiratory volume in one second of 0.5 +/- 0.2 L (22 +/- 9% of predicted) and St. George's Respiratory Questionnaire total score of 61 +/- 14. The mean 24-h arterial oxygen saturation measured by pulse oximetry (Sp,O2) was within normal limits (94 +/- 1%), but mild hypoxaemia with a mean Sp,O2 of 89 +/- 4% and a total of 12 +/- 15 desaturation episodes per patient were observed, mostly during daily activities. Multiple regression analysis revealed no significant predictors for patient oxygenation. In summary, 24-h pulse oximetry showed adequate oxygenation in this group of COPD patients on LTOT, though mild hypoxaemia was present during some daily activities.