We develope core-shell systems with a hydrophilic shell and a hydrophobic core. The particles are formed by self organization. Furthermore we are able to create vesicles, which can be varied in size during the self assembly process. The vesicles have a liposome like structure. The particles seize varies between 20 and 100 nm. But even particles with a size as large as 200 nm can be synthesized. The hydrophilic core is synthesized by the reaction of reactive ester polymers with hydrophilic amines such as 1-aminoisopropanol. The reactive ester can be also used to attach recognition structures and polymer markers. We are working with two groups of markers. The first ones are fluorescence markers with can be used for in vitro studies. The second group consists of radioactive markers which can be used for in vivo studies. We want to achieve a deeper understanding of organic nanoparticles and to investigate their movement and enrichment in the living organism by PET studies.