Liquid pharmaceutical formulation for prolonged release of interleukin (s), said formulation comprising at least one interleukin, possibly at least one other active ingredient (PA), preferably in aqueous solution, and a colloidal, aqueous suspension of low viscosity , based on sub-micronic particles of biodegradable, water-soluble polymer (PO) selected from the group consisting of polyamino acids, polysaccharides, gelatins or mixtures thereof and carrier of hydrophobic groups (GH), said particles being associated non-covalently with said interleukin and eventually said other active principle (PA), characterized in that: - because the dispersing medium of the suspension is essentially constituted by water, - because its concentration in [PO] is set to a value [PO] - 0, 9.C1 so that said Pharmaceutical formulation is appropriate to be injected parenterally and then form a gelled reservoir in vivo, repress C1 being the concentration of "induced gelation" of the PO particles as measured in a GI test as described in the description, whose formation of gelled deposit: or is, on the one hand, at least partly caused by at least one physiological protein present in vivo, or and allowing, on the other hand, to prolong and control the duration of leucine release and possibly PA in vivo, beyond 24 hours after administration, - it is liquid under injection conditions. , - and is also liquid at the physiological temperature and / or pH, and / or in the presence: * of physiological electrolyte in physiological concentration, * and / or at least one surfactant.Formulación farmacéutica líquida para la liberación prolongada de interleucina (s), comprendiendo dicha formulación, como mínimo, una interleucina, eventualmente, como mínimo, otro principio activo (PA), preferentemente en solución acuosa, y una suspensión coloidal, acuosa, de baja viscosidad, a base de partículas submicrónicas de polímero (PO) biodegradable, hidrosoluble seleccionado del grupo que consiste en poliaminoácidos
