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) the 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.
