The solubility of the drug sulfathiazole has been measured in pure and methanol modified CO2. Temperatures were varied between 298 and 353 K and pressures between 10 and 20 MPa. Methanol mole fractions were varied between x(MeOH) = 0-0.15. Solubility of sulfathiazole was found to be between x(STZ) = 1.2 x 10(-9) to 1.5 x 10(-5) depending on the composition of the fluid phase and operating temperature and pressure. Additionally, the solid-vapor equilibrium of the ternary system was determined with a high pressure view-cell at 3 5 3 K and 10 MPa. The experimental data were used to construct ternary Gibbs-triangles at constant temperature and pressure. The Gibbs-triangles were used to determine the experimental conditions for subsequent crystallizations of sulfathiazole from a saturated methanol solution using supercritical CO2. Size, morphology and yield of the particles were related to the experimental conditions. The impact on processing conditions in supercritical fluid processes for particle design has been assessed.