No / Purpose The relative lung bioavailability of salbutamol sulfate particles produced using supercritical fluids (SEDS¿) and delivered by dry powder inhaler (DPI) was compared with the performance of a conventional micronized drug DPI using the same device design (Clickhaler¿, Innovata Biomed). Materials and Methods Twelve healthy volunteers and 11 mild asthmatic patients completed separate four-way randomised cross-over studies, assessing the relative bioavailability of salbutamol sulfate (urinary excretion method), formulated as SEDS¿ particles (three batches) and micronized particles (Asmasal¿ inhaler, UCB Pharma Ltd). Post-treatment improvements in patient lung function were assessed by measuring FEV1. Physicochemical evaluation of the three SEDS¿ batches revealed inter-batch differences in particle size and shape. Results There was no significant difference in the relative lung bioavailability of salbutamol and its bronchodilator response between the best performing SEDS¿ formulation and the Asmasal¿ inhaler in volunteers and patients, respectively. SEDS¿ salbutamol sulfate showing wafer like morphology gave greater fine particle dose, relative lung bioavailability and enhanced bronchodilation compared to other SEDS¿ batches containing elongated particles. Conclusions Active Pharmaceutical Ingredient (API) manufactured using supercritical fluids and delivered by DPI can provide similar lung bioavailability and clinical effect to the conventional micronized commercial product. Product performance is however notably influenced by inter-batch differences in particle characteristics.