Ibuprofen (a chiral nonsteroidal antiinflammatory drug) is micronized via the Rapid Expansion of the Supercritical CO2 Solution (RESS) process. Experiments are conducted to investigate the effects of extraction pressure (130-170 bar), pre-expansion temperature (76-104 degreesC), capillary length (8 and 12 mm), spraying distance (20-60 mm), and collision angle (45 and 90) on the size and morphology of the precipitated Ibuprofen particles. The characterization (size, morphology and crystallinity) of the particles is carried out using scanning electron microscopy (SEM), and X-ray diffraction (XRD) measurements. The average particle size of the original material is 45 mum (+/- 1.51), while the average particle size of Ibuprofen after micronization via the RESS process is between 2.85 mum (+/-0.31) and 7.48 mum (+/-0.54) depending upon the experimental conditions used. The degree of crystallinity of Ibuprofen is slightly reduced after processing with the RESS process compared to the original material. No clear dependence of the particle size on the extraction pressure is observed, whereas an increase in the spraying distance increases the particle size. However, increases in the pre-expansion temperature, capillary length, and collision angle have reducing effects on the average size of Ibuprofen particles collected. (C) 2002 Published by Elsevier Science B.V.