The manufacture of fine particles of two steroid drugsprogesterone and medroxyprogesterone acetatehas been investigated through the rapid expansion of supercritical solutions (RESS). The motivation was the production of particles with improved characteristics for use in the pharmaceutical industry. Solubility data for each drug in supercritical CO2 were measured prior to performing the RESS experiments as these data are essential for accurate experimental design. The solubility data were measured using a dynamic apparatus at pressures between 100 and 240 bar and at 313.1 and 333.1 K. Particles were manufactured by expanding a solution of supercritical CO2 saturated with drug through a micronozzle to pressures of 50 bar or less. A sufficient amount of particles was manufactured to allow particle characterization tests to be completed. Particle size, particle size distribution, and specific surface area were used as assessment measures to compare the product samples obtained in different experimental conditions. The RESS technique produced particles that were significantly smaller than existing samples manufactured using jet-milling.