Expectoration of mucus is important in preventing the development of airway inflammation in patients with diffuse panbronchiolitis (DPB). To evaluate the clinical efficacy of the FLUTTER device in clearing mucus from the airways of patients with DPB who have difficulty expectorating, we assessed pulmonary function and symptoms in patients treated with FLUTTER. Eight patients in a stable clinical condition with DPB were included in the study. The study was divided into two consecutive, 1-week periods. The initial week was an observation week. During the following week, patients used FLUTTER four times daily. Expectorated sputum was collected in a container and weighed every day during 2 weeks. Pulmonary function, partial oxygen pressure and partial carbon dioxide pressure in arterial blood were measured in all patients on the last day of the observation week and the FLUTTER treatment week. A symptom score for difficulty of expectoration was determined by questionnaire. A pneumothorax developed in one patient during using FLUTTER. The mean daily sputum weight and peak expiratory flow rate increased significantly after treatment with FLUTTER ( P< 0.04 and P< 0.02, respectively). Symptom score improved significantly after using FLUTTER ( P< 0.02). We conclude that the use of FLUTTER is effective in clearing mucus from the airways. However, the development of a pneumothorax may complicate use of the procedure in some cases.