Polycations such as PEI (poly(ethyleneimine)) and PDMAEMA (poly(2-dimethylamino) ethyl methacrylate) are commonly used in non-viral gene delivery. Differences in efficiency exist, but comparative experiments on DNA compaction, cellular uptake, cellular trafficking and finally nuclear entry are largely lacking. in this study, ATRP (atom transfer radical polymerization) was used to synthesize three highly defined structures of PDMAEMA (linear, highly-branched, and star-shaped), which were systematically compared to linear and branched PEI. For the investigation of intracellular trafficking, polymers were fluorescently labelled. The ability to compact DNA and cellular uptake efficacy were similar for all investigated polycations. Transfection efficiencies at optimized N/P ratio showed similar trends as cytotoxicities of the free polymers, with the star-shaped PDMAEMA reaching almost similar orders of transfection efficiencies as branched PEI. Twenty-four hours post-transfection, polymer fluorescence was almost exclusively found in close proximity (but never inside) the nucleus. In case of the 'good' transfectants (PEI, star-shaped PDMAEMA), the fluorescence concentrated in 'spots' of high intensity, arguing for localization in specific sub-cellular structures. (C) 2009 Elsevier Ltd. All rights reserved.