Inhaled corticosteroids are first-choice drugs in the treatment of chronic asthma. A metered dose inhaler (MDI) equipped with a spacer device is easier to use for patients with a poor inhalatory technique; it favors a reduction in the size of the particles delivered to the patient and thus a reduction in the incidence of local and systemic side effects of these drugs. The aim of this study was to determine the particle characteristics of fluticasone propionate (FP), flunisolide (FLUN), and beclomethasone dipropionate (BDP), each administered at a rate of 250 micrograms per puff and at inspiratory flow rates of 30 and 60 L/min in vitro, to estimate the particle characteristics of these drugs aspirated via an MDI alone and via a large-volume holding chamber (Volumatic). Compared with the MDI alone, at 30 L/min, the Volumatic (Glaxo Wellcome, Ware, UK) significantly reduced the mass median aerodynamic diameter (MMAD) and increased the fine particles (< 5 microns and < 2 microns) generated by all three drugs. At 60 L/min, the MMAD increased and the generation of fine particles decreased with both devices. These data suggest that the inspiratory flow applied by means of the devices may be a determinant for the deposition of the drug in the lower airways in that by increasing the inspiratory flow, the MMAD increases and the percentage of fine particles decreases, probably because of the reaggregation favored by the higher flows.