BACKGROUND: Lung mucociliary clearance is impaired in patients with chronic obstructive pulmonary disease (COPD). Treatment guidelines recommend that patients with COPD receive maintenance therapy with long-acting beta-agonists and anticholinergic agents. METHODS: Twenty-four patients with mild to moderate COPD received formoterol (12 μg, twice daily from Turbuhaler® dry powder inhaler (DPI)) or tiotropium (18 μg, once daily from Handihaler® DPI) for 14 days. They also received single doses of formoterol, tiotropium, salbutamol (200 μg) and placebo. A radioaerosol technique was used to assess the effects on mucus clearance of 14 days treatment with formoterol or tiotropium, as well as single doses of these drugs. RESULTS: The 4 h whole lung retention of radioaerosol was significantly higher after 14 days treatment with tiotropium (P = 0.016), but not after 14 days treatment with formoterol. However, patients bronchodilated after 14 days treatment with both drugs, so that the deposited radioaerosol may have had an increased distance to travel in order to be cleared by mucociliary action. A single dose of formoterol enhanced radioaerosol clearance significantly compared to other single dose treatments (P < 0.05). CONCLUSION: Formoterol (12 μg) enhances mucus clearance in patients with mild to moderate COPD when given as a single dose, and may do so when given for 14 days. Studies of longer duration would be needed in order to assess the effects of the study drugs on mucus clearance when they are used for long-term maintenance therapy.