Supercritical Assisted Atomization (SAA) has been used to produce lysozyme microparticles. Lysozyme has been micronized using water, buffered water at pH 6.2 and water-ethanol mixtures at different volume percentages. Precipitated lysozyme particles were spherical, with a narrow particle size distribution (PSD) ranging from 0.1 to 4 mm. The concentration of lysozyme in the liquid solvent mixture had a nonlinear effect on the particle distribution, with an increase of the X-0.9 from about 1 to 3 mu m varying the enzyme concentration from 5 to 20 mg/mL. Precipitation temperature was set as low as possible to avoid enzyme degradation. High-performance liquid chromatography analysis showed no degradation of lysozyme and the enzyme activity, measured by turbidimetric enzymatic assay, only slightly decreased after SAA processing. Depending on the process conditions lysozyme retained from 95% to 100% of the biological activity compared to the untreated enzyme. Biotechnol. Bioeng. 2009; 104: 1162-1170. (C) 2009 Wiley Periodicals, Inc.