||The performance of pressurized metered dose inhalers (pMDIs) and spacers in correct dose recommendations is important, but limited information on dose delivery and fine-particle dose from different combinations of spacers and pMDIs is available. In this study, three combinations of spacers and pMDIs were investigated: NebuChamber and AeroChamber with budesonide pMDI and Babyhaler with fluticasone propionate pMDI. Doses were withdrawn onto a filter either with a breathing simulator (dose to ventilator) or with constant flow (maximal dose). The fine-particle dose was assessed with a cascade impactor (Andersen Sampler). The effect of repeated use and cleaning of the spacers on the passive fallout of aerosol within the spacers was determined by evacuating the dose on a filter 2, 5, 10 and 30 s after actuating the spray. The drugs were quantified by liquid chromatography. The NebuChamber delivered the highest doses, both maximal dose and dose to ventilator. The recovered doses (means+/-SD) were 55+/-6% and 51+/-2%, respectively, of the delivered dose from the pMDI. The corresponding results for the Babyhaler were 41+/-7% and 24+/-4% and for the Aerochamber 27+/-3% and 17+/-3%. The passive fallout of aerosol, determined as half-life (t1/2) was around approximately 30 s for the NebuChamber, 9-15 s for the Babyhaler and approximately 10 s for the AeroChamber. The present study confirms that there are significant differences in dose output from different combinations of pressurized metered dose inhalers and spacers, with the NebuChamber giving the highest dose, both as delivered dose and in droplets <4.7 microm. Interactions with the spacer material, dead space in the inspiratory line and entrainment of air during inhalation due to inefficient valve control could account for these differences.