Receptor-mediated gene transfer is an attractive method for the targeting of DNA in specific tissues. Membrane lectins have been found at the surface of many cells and are good candidates for gene transfer by DNA-glycoconjugate complexes as specific carriers. However, to be useful for gene therapy, it is critical that the DNA be complexed and aggregated in very small particles. We describe here the properties of a new polycationic polynorbornene, with lactobionate counterions, that spontaneously forms small and stable latexes in water. Furthermore, because of lactobionate effect, the complexation with DNA lead to highly compacted aggregates with a diameter of around 10-20 nm. By the use of transmission electron microscopy, gel electrophoresis, and zeta potential measurements, we have studied both polymer organization and DNA-polymer complex formation.