Metered inhalers using chlorofluorocarbon (CFC) propellents have been gradually replaced by new devices that use hydrofluoroalkanes (HFAs) as their propellents, which are less harmful to the environment. This reformulation led to a substantial improvement of the previous technologies applied to inhalation devices and of the physical characteristics of drugs delivered. In particular, inhaled corticosteroids, such as beclomethasone dipropionate (BDP) which is of fundamental importance in the long-term management of bronchial asthma, took advantage of this reformulation. Unlike the preparation beclomethasone dipropionate and chlorofluorocarbon (BDP-CFC) which was a suspension, that of beclomethasone dipropionate and a hydrofluoroalkane (BDP-HFA) is a solution and produces an aerosol with a mean aerodynamic particle size of 1.1 microm, which is much smaller than the particle size of 3.5-4.0 microm, obtained with the BDP-CFC. The particles of BDP-HFA can then deposit in the lungs in a larger amount, and particularly in the more peripheral airways where the inflammatory process starts in the case of bronchial asthma. A 12-week use of BDP-HFA ensured a significant better control of the bronchial response to methacholine (MCh) than the corresponding use of BDP-CFC for the same duration. The therapeutic performance of BDP-HFA proved much higher and allowed the substantial reduction of the therapeutic daily dose for the clinical asthma management, being the increased and more peripheral deposition of BDP-HFA is presumed to play a crucial role.