A process for preparing particles of a substance, such as a protein or polypeptide, comprising: (a) preparing a first liquid comprising water, the substance and a modulator, wherein the modulator has a solubility in water which decreases with increasing temperature; and (b) contacting the first liquid with a second liquid comprising a fluid gas and an organic solvent using an anti-solvent fluid gas technique under conditions of temperature and pressure which result in the precipitation of particles comprising the substance, wherein the temperature of the first liquid is at or above the cloud point temperature of the first liquid when the first liquid contacts the second liquid. Also claimed are particles obtained according to the process and compositions containing the particles.