Abstract: The present invention relates to novel pharmaceutical formulations based on stable, fluid aqueous colloidal suspensions for the prolonged release of an interleukin (IL) (and one or more other possible active principles), and to the applications, especially therapeutic applications, of these formulations. The object of the invention is to propose a fluid pharmaceutical formulation for the prolonged release of interleukin(s) (and one or more other possible active principles) that makes it possible, after parenteral injection, significantly to increase the in vivo release time of the IL while at the same time reducing the plasma concentration peak of this IL, said formulation furthermore being stable on storage and also being biocompatible, biodegradable, non-toxic and non-immunogenic and having a good local tolerance.