Abstract: A method for promoting entry of an agent (introduced agent) into a cell, the method comprising the step of complexing the introduced agent in the presence of an entry-promoting agent and then exposing to cells, wherein the entry-promoting agent comprises a linear and/or branched or cyclic polymonoguanide/polyguanidine, polybiguanide, analogue or derivative thereof according to the following Formula 1a & b. The method also provides a means for formation of nanoparticles formed between the entry promoting agent and the introduced agent.