Abstract: A process for the production of particles comprises the steps of formation of a solution of a desired substance in a suitable solvent; ii)generation of an aerosol from the solution of said substance; iii) collection of the aerosol droplets in a vessel containing a non-solvent of said substance; and iv) application of ultrasound to the droplets dispersed in the non-solvent to effect crystallisation of said substance. The particles produced find application in for example pharmaceutical and agrochemical formulations, especially in inhalation formulations.