Several in vitro methods have been proposed to simulate the dissolution of inhaled powder drugs in the lungs. These methods prescribe that the aerosol to be tested is collected on a solid surface and then contacted with a liquid dissolution medium. One important question is how to coat the test surface with aerosol in order to prepare for a dissolution experiment that will be as relevant as possible to the in vivo process. Three important aspects of the aerosol coating process are i) the density of deposition of aerosol on the test surface, ii) the deposition pattern aerosol on the test surface, and iii) the relation between the particle size distribution of the tested airborne aerosol and the particle size distribution of the aerosol deposited on the test surface. For two different formulations of the same low-soluble substance it remains unknown to what extent the same dynamic solubility measured in vitro will be accompanied by the same PK pattern following in vivo inhalation exposures.