A suspension of biocompatible particles based on a double-block hydrophilic neutral polyminoacid/hydrophobic neutral polyaminoacid copolymer and suitable for carrying active principles. The carrier particles can combine in colloidal suspension in a non-dissolved state with an active principle and release same, particularly in vivo, in prolonged and/or delayed delivery. The carrier particles may be derived from a powdery solid, and spontaneously form stable aqueous suspensions in the absence of surfactants or organic solvents. The invention also concerns the carrier particles in dry form, the method of preparing them, and pharmaceutical compositions (in dry form or suspension) which include the carrier particles associated with an active principle.