Poly (D, L lactide-co-glycolide) and poly (D, L lactide) microparticles were prepared by solvent evaporation and the process reproducibility was evaluated in terms of the loading of a model protein into the microparticles, the microparticle size and the in-vitro release profiles of the protein. The results showed that the microencapsulation method allowed the preparation of microparticles with mean sizes from <0.5 mu m to 100 mu m in size, with protein entrapment from 0.5 to 5%w/w. The microparticles were smooth and free from surface defects. Moreover, the reproducibility of the preparation method was demonstrated by the in-vitro release profiles obtained using different batches of microparticles prepared under similar conditions and by the reproducibility of microparticle size and protein loading. The results demonstrated that the preparation method was both robust and reproducible and allowed the preparation of microparticles with desired characteristics in terms of loading levels, particle size and release rates.