A process for preparing microparticles comprising a biologically active material and a polymer and having an average particle size expressed as the average volume diameter (DMV) of 10 to 500 µm, in which the biologically active material is substantially insoluble in the polymer, process comprising: a. contacting a mixture of the biologically active material or a precursor thereof, the polymer or a precursor thereof and a processing aid with a supercritical fluid that is capable of swelling the polymer under conditions of temperature and pressure necessary to keep the fluid in a supercritical state； b. allow the supercritical fluid to penetrate and liquefy the polymer, while maintaining the temperature and pressure conditions, so that the fluid is maintained in a supercritical state, and to combine or mix the supercritical fluid and the liquefied polymer； C. remove the combined mixture from a mixing chamber that is in supercritical conditions to an independent container, which is not in supercritical conditions, through a nozzle or a similar orifice, where the processing aid is selected from: (i) esters of fatty acid consisting of mono and polyglycol diesters of 12-hydroxystearic acid and about 30% free polyethylene glycol, and sorbitan monooleate； (ii) 2-pyrrolidone, N-methyl-2-pyrrolidone and pyrrolidone polymers； (iii) polypropylene glycol； (iv) mono-, di- and medium chain triglycerides having a formula (CH2OR1) (CH2OR2) (CH2OR3) in which R1, R2 and R3 are independently H or -C (O) (CH2) nCH3 (where n >； = 6 to 8), provided that not all of R1, R2 and R3>； = H； and (v) poloxamers having a general formula HO (C2H4O) a (C3H6O) b (C2H4O) aH, in which a is normally from 2 to 130 and b is normally from 15 to 67.Un proceso para preparar micropartículas que comprenden un material biológicamente activo y un polímero y que tienen un tamaño medio de partícula expresado como el diámetro medio en volumen (DMV) de 10 a 500 μm, en el que el material biológicamente activo es
