RESS (Rapid Expansion of Supercritical Fluids) was used to micronize and stabilize organic substances. Pure substances used were benzoic acid, Ibuprofen, Griseofulvin, Phytosterol and polylactic acid. Furthermore Phytosterol was stabilized using polylactic acid and Eudragit L100-55. In all cases particled with diameters of less than 200 nm could be produced. Pre-expansion pressures ranged from 10 to 30 MPa and temperatures from 323 to 418 K. Mainly carbon dioxide was used as solvent.