Mucus retention in the lungs is a feature of several chest diseases. It is unclear to what extent suboptimal mucus transportability is responsible for the poor clearance of lung secretions. We described a new model, the mucus-depleted bovine trachea, for measurement of the ciliary transportability of respiratory mucus. Mucus depletion was demonstrated microscopically and functionally, and it was accomplished by simple physical means without impairing ciliary action. Control mucus from the tracheas of humans and animals was transported rapidly on this system. However, sputum from 54 patients with bronchiectasis was transported slowly, at a mean of 15% of the rate of control mucus. There was no correlation between sputum transportability and either purulence or the presence of Pseudomonas aeruginosa. This work suggests that there is a serious defect in the ciliary transportability of sputum that is unrelated to the presence of infection. The model should allow in vitro assessment of agents designed to aid mucociliary clearance.