Abstract: The invention relates to a method of obtaining micro- and nanometric polymeric particles in a controlled, reproducible manner. The aforementioned particles have a spherical shape and a very narrow, uniform size distribution. The invention comprises the use of an easy particle-forming method consisting in using hydrodynamic forces to focus a composite microjet formed by two concentric fluids and can be used in the encapsulation of fragile compounds of biological interest, from peptides and proteins to cells and micro-organisms.