The Flutter is a handheld device designed to facilitate clearance of mucus in hypersecretory lung disorders. Exhalation through the Flutter results in oscillations of expiratory pressure and airflow, which vibrate the airway walls (loosening mucus), decrease the collapsibility of the airways, and accelerate airflow, facilitating movement of mucus up the airways. We studied 18 patients with cystic fibrosis and mild to moderate lung disease to determine the efficacy of the Flutter in clearing mucus from the airways. The amount of sputum expectorated (measured by weight) when the Flutter was used was compared with the amount expectorated with vigorous voluntary coughing and with postural drainage (chest percussion and vibration). The amount of sputum expectorated by subjects using the Flutter was more than three times the amount expectorated with either voluntary cough or postural drainage (p < 0.001). There were no adverse effects. The Flutter is simple to use, inexpensive, and fully portable, and once the patient and family are instructed in its use, it does not require the assistance of a caregiver. For hospitalized patients, elimination of the need for a therapist could reduce health care costs. Long-term studies of the use of the Flutter seem justified to determine its effects on pulmonary function and outcome.