New drug delivery systems (DDS) are described containing hyaluronic acid and a therapeutic agent, wherein the therapeutic agent is linked, directly or via a linker, to 6-aminohyaluronic acid and where the linkage of the drug or linker with 6-aminohyaluronic acid is realised by an amide bond. Preferred therapeutic agents for use in the present DDS are anti-inflammatory, antibiotic, antitumor drugs. Preferred linkers are: succinic acid, succinic acid linked to aminoacids, succinic acid linked to peptides. The DDS are stable and free of undesired reaction by-products and impurities, and show a high level of pharmacological efficacy.