- Introduction Synthetic DNA delivery agents are an importante alternative to viral vectors, since they display less immunogenicity and propagation risks . However, non-viral DNA delivery agents display in many cases high toxicity. This is especially significant in the case of polymeric cations such as polylysine and dendrimers. The integration of a biodegradable entity into non-viral gene delivery systems promises decreased toxicity and improved gene expression . We have designed and synthesized biodegradable polymers derived from Lys, Arg and His of various lengths containing disulfide bridges along their backbone. Additionally, a biodegradable dendrimer using the same approach was synthesized.