In subjects with an inherited lack of mucociliary transport, so called immotile-cilia syndrome (ICS), coughing effectively clears particles deposited in larger airways of the tracheobronchial region. The present study investigated clearance in smaller airways of 111In-labeled 6-microm (aerodynamic diameter) monodisperse Teflon particles in six subjects with ICS. The particles were inhaled at an extremely slow flow, 0.05 L/s. Theoretical calculations and experimental data in healthy subjects using this slow flow support particle deposition mainly in smaller ciliated airways, i.e., in bronchioli (generations 12-16). This contrasts with the more centrally deposited pattern obtained using a normal inhalation flow, 0.5 L/s. Lung retention was measured at 0, 24, 48,72 and 96 h. Clearance was significant every 24 h measured over the first 72 h, whereupon it slowed down. The fractions of retained particles were significantly (p < .01) larger than those found for healthy subjects using the slow inhalation flow and those found for ICS subjects using a normal inhalation flow. The results indicate that clearance of particles in smaller airways is incomplete and that cough cannot fully compensate for the lack of mucociliary transport in this region.