The purpose of this study was to understand the kinetics of emptying of micronised salbutamol sulphate (SS) and lactohale 300 (LH300) under varying air flow rates (30-180 L mm(-1)) from three dry powder inhaler devices, Rotahaler (R) (RH), Monodose Inhaler (R) (MI) and Handihaler (R) (HH). Aerosol concentration vs. time profiles, determined through real-time laser diffraction particle sizing, demonstrated that the majority of the powder from RH was emitted within one second while a more prolonged aerosolisation was observed from MI and HH. Peak aerosol concentrations were achieved more rapidly from RH compared to MI for both SS and LH300. Calculated cumulative emitted mass (CCEM) vs. time profiles were obtained from the aerosol concentration vs. time profiles and the emitted mass and the rate of CCEM (k(CCEM)), estimated from a modelling approach, increased with increasing air flow rates. The k(CCEM) vs. air flow rate profiles of SS and LH300 were significantly different at high air flow rates. The k(CCEM) was highest from RH and lowest from MI. Differences in k(CCEM) between the devices were related to capsule aperture size while the differences between the materials were due to the powder bed structure. This approach provided an understanding of the rate at which powder mass emptied from dry powder inhaler devices and was proposed to be a powerful development tool for the future powder inhalers. (C) 2011 Elsevier Ltd. All rights reserved.