Complexation and aggregation of DNA. in small particles are the bases of efficient vehicles for gene delivery. The aggregation properties of new linear polycationic polynorbornene polymers with acetate counterions are described. These polymers spontaneously form stable latexes in water, offering a large cationic surface for favorable adsorption of DNA. Furthermore, such polymers are able to bind and efficiently compact the DNA into very small aggregates because of cationic charges and the hydrophobic packing of norbornane units. By use of transmission electron microscopy, atomic force microscopy, gel electrophoresis, and zeta potential measurements, we have studied both the polymer organization and the DNA-polymer complex formation.