3. Endoscopic Bronchoscopy An operator approved by the Royal Brompton Ethics Committee will perform all bronchoscopies. The bronchoscopist that will perform these procedures is Dr Borja Cosio. Subjects will attend the bronchoscopy suite at 8.30 am after having fasted from midnight. Subjects will have pre-treatment with atropine (0.6 mg iv) and midazolam (5-10 mg iv). Oxygen (3 l/min) will be administered via nasal prongs throughout the procedure and oxygen saturation monitored with a digital oximeter. Using local anaesthesia with lidocaine (4%) to the upper airways and larynx, a fibreoptic bronchoscope (Olympus BF10 Key-Med) will be passed through the nasal passages into the trachea. Bronchoalveolar lavage (BAL) will be performed from the right middle lobe using warmed 0.9% NaCl with 4 successive aliquots of 60 ml. This is well-tolerated in subjects with COPD. Patients may experience pharyngeal irritation following the procedure; there is a 5% chance of fever following the procedure. Subjects undergoing bronchoscopy for clinical reasons will also be included in this study.