Abstract: The present invention relates to a drug carrier system comprising a plurality of colloidal particles having a core and a shell, said particles being comprised of copolymer molecules, which copolymer comprises at least one A block and at least one B block different from the at least one A block, wherein the at least one A block consists of a polymer unit of a first set of monomers and the at least one B block consists of a second set of monomers. In addition, the invention relates to block copolymers that are useful in this system, as well as pharmaceutical compositions based on said colloidal system.