A pilot plant is presented which has been built to prepare fine particles by rapid expansion of supercritical solutions (RESS process). This technique offers interesting applications for products that are produced in small amounts, such as certain pharmaceuticals or energetic materials. For the presented research, cholesterol was used as a model substance for pharmaceuticals. Our measurements were carried out with two different Laval nozzles with a 100 and 150 mu m diameter, respectively In contrast to investigations of other groups the scale of the plant is larger which results in a higher flow and production rate. The mean size of the particles measured by photon correlation spectroscopy (PCS) was about 400 nm. The influence of the extraction temperature, pre-expansion pressure and nozzle diameter on the particle size is not very marked and systematic.