The system of mucociliary clearance has the important task to remove from the airways inhaled substances and locally formed secretions. Inborn disorders of the mucociliary transport are the result of ciliary dysfunction (primary ciliary dyskinesia) or of increased viscosity of the bronchial secretions (mucoviscidosis). By far more frequency however are acquired disturbances. Inflammation of the airways results nearly always in disorder of the mucociliary transport which in early stages is reversible. With morphologic lesions, the disturbance may become irreversible. Infectious inflammations, especially those by rhinoviruses and mycoplasma, are causing ciliostatic and ciliotoxic alterations which may disturb the mucociliary clearance up to one year following the infection. Noninfectious inflammation is at first accelerating the transport of mucus through the action of cells of the body itself, especially granulocytes and eosinophiles and mediators liberated from them. Probably, these are causing a cilioexcitation which is later followed by a long-lasting depression of the mucociliary transport caused by production of mucus with high viscosity. Therapeutic measures consist in an early anti-infectious treatment and in the stimulation of the frequency of ciliary beating by beta-adrenergic drugs.