A special inhalative device is described for reproducible deposition patterns of radioactive aerosols to measure mucociliary and tussive clearance and to evaluate the effect of drugs on the bronchial tree. Additive actions on mucus transport exist between beta 2-agonists and theophylline, but not in combination with inhalative quaternary ammonium compounds (ipatropium and oxitropium bromide). Mucolytics are generally less effective on mucociliary clearance than beta 2-agonists and theophylline, positive, negative and nonresponders are often seen due to the different viscoelastic properties of the mucus. Mucus transport is more than mucociliary clearance. Two-phase gas/liquid movement and coughing are also important transport mechanisms for bronchial mucus. Therefore, bronchodilators enhance mucus transport by increasing airway patency, which increases total and regional air flow and improves cough clearance.