A liquid pharmaceutical formulation (I) for prolonged release of active agent(s) (A) comprises a low viscosity aqueous colloidal suspension of submicron particles of water-soluble, biodegradable polymers (II) carrying hydrophobic groups, non-covalently associated with (A), where on parenteral injection (I) forms a gelled depot for prolonging the duration of (A) release to more than 24 hours. A liquid pharmaceutical formulation (I) for prolonged release of active agent(s) (A) comprises a low viscosity aqueous colloidal suspension (with water as dispersion medium) based on submicron particles (SMP's) of water-soluble, biodegradable polymers (II) carrying hydrophobic groups (HG's), non-covalently associated with (A). On parenteral injection, (I) forms a gelled depot in vivo (at least partially due to physiological proteins), controlling and prolonging the duration of (A) release to more than 24 hours. (I) is liquid under the injection conditions； at physiological temperature and/or pH； and/or in presence of physiological electrolytes at physiological concentrations and/or surfactant(s). Independent claims are included for: (1) a variant of (I) as described above, where the duration of release of (A) is not restricted but the concentration of (II) is sufficiently high to form a gelled depot in vivo in presence of protein(s) after parenteral injection； (2) novel derived products (preferably in powder or gel form), consisting of SMP's formed by non-covalent association of (II) and (A) as above and obtained from (I)； and (3) methods of preparation of (I).
