Bronchoscopy with broncho-alveolar lavage is a diagnostic tool in patients with pneumonia. Especially patients with acute or chronic pulmonary diseases are at risk of respiratory failure during or after bronchoscopy. It is known that in these cases bronchoscopy can be performed safely using non-invasive ventilation. It seems probable that high-flow oxygen, which is used in the treatment of patients with hypoxemic respiratory failure, is equally effective in preventing the development of respiratory failure during fiberoptic bronchoscopy while improving patient comfort. In this prospective randomised study the safety of high-flow oxygen is compared with non-invasive ventilation in patients with hypoxemic respiratory failure undergoing fiberoptic bronchoscopy.