Inhaled dry powder mannitol is well established for use in bronchial provocation testing. Inhaled mannitol also increases mucociliary clearance, and therefore could have a role in treating chronic suppurative lung disease. There have been a number of studies in cystic fibrosis and bronchiectasis. An international Phase III trial has just been published that suggests the use of regular inhaled mannitol increases lung function and reduces exacerbation frequency in cystic fibrosis. Inhaled mannitol exerts its effects in a number of ways, most importantly like hypertonic saline, setting up an osmotic gradient so water flows into the airway lumen, increasing mucus hydration and mucociliary clearance. Its formulation as a dry powder makes it quick and convenient to take.