A novel process configuration of supercritical assisted atomization (SAA) was used to produce microparticles of two model thermolabile compounds: poly L-lactide (PLLA) and bovine serum albumin (BSA). This new configuration allowed to operate the precipitation process below the atmospheric pressure, to perform the drying process at lower temperatures without any damage to thermolabile materials. Process parameters, such as gas to liquid ratio and precipitation temperature, were investigated to evaluate their influence on particle size and morphology. Well defined spherical particles were produced. PLLA microparticles coalescence was avoided using a precipitation pressure from 0.65 to 0.5 bar producing particles with a mean diameter between 1 and 1.5 mu m, and a standard deviation of about 0.4. BSA spherical particles with a mean diameter of about 1 mu m and a standard deviation of about 0.7, were obtained operating at 0.8 bar in the precipitator. Fourier transform infrared analysis on BSA micropartides revealed that no modification on protein secondary structure took place during SAA process, thus, protein denaturation was avoided. (C) 2011 Elsevier B.V. All rights reserved.