OBJECTIVES: The objectives of this study were to determine the bronchial mucus transport velocities in ventilated ICU patients and to study the possible role of impaired mucus transport in the development of retention of secretion and pneumonia. DESIGN: The patients were studied prospectively in a convenience sample trial. SETTING: The study took place at a university hospital. PATIENTS: Thirty-two ventilated patients in a surgical ICU were included in the study. The study was approved by the Ethics Committee of the University of Ulm. INTERVENTIONS: Bronchial mucus transport velocity (BTV) was measured with a small volume of technetium 99m-labeled albumin microspheres within the first 3 days of mechanical ventilation. The radiolabeled bolus was deposited at the distal end of the right and left main bronchus via flexible bronchoscopy. The movement of the microspheres toward the trachea was visualized and recorded using a scintillation camera. After determination of BTV, the patients were examined daily for 4 days to record pulmonary complications (defined as retention of secretion and nosocomial pneumonia). MAIN MEASUREMENTS AND RESULTS: The median BTV in the right primary bronchus was 0.8 mm/min and in the left it was 1.4 mm/min. In nine patients both radioactive drops remained at the application site. In 14 patients, a total of 19 pulmonary complications occurred (10 times retention of secretion, 9 times pneumonia). Patients with pulmonary complications had statistically significant lower BTV compared with patients without pulmonary complications; in the left bronchus 0 (0 to 6.5) mm/min (median with range) vs 3.5 (0 to 10.5) mm/min (p < 0.01) and in the right bronchus 0 (0 to 3.0) mm/min vs 4.7 (0 to 11.7) mm/min (p < 0.01). CONCLUSIONS: Ventilated patients in the ICU frequently have impaired mucus transport, which is associated with the development of retention of secretion and pneumonia.