The pressurised metered-dose inhaler (pMDI) is a compact pressurised spray dispenser designed for the oral inhalation of multiple doses of finely dispersed drug in the treatment of various pulmonary diseases, the most common being asthma. This research was concerned with the experimental investigation of the spray issued from a pMDI and has been motivated by the urgent need to find suitable replacements to the environmentally destructive CFC-based propellants currently used in the device and to further the understanding of the mechanisms of atomization. The experimental work was conducted using 1-D phase-Doppler particle analyser (PDPA), yielding the most detailed temporal and spatial analysis of the pMDI spray to date. Two formulations were studied to compare the performance of an 'ozone-friendly' hydrofluoroalkane propellant against that of a traditional placebo CFC-based mixture. The PDP A analysis was complemented by a visual investigation of the near-orifice flow field using copper laser-strobe microcinematography in an attempt to obtain information on the primary atomization process of the pMDL This work was conducted in parallel with the theoretical investigation of the spray issued from a pMDI.