The main limitation of non-viral gene transfer methods is their relatively low efficiency in vivo. However, a number of approaches can be taken to improve their performances, whether the aim is studying gene function during development or employing these techniques for gene therapy. Three non-viral delivery systems that we have been particularly involved in in developing are described: the cationic lipid, dioctadecylamidoglycylspermine (DOGS), the cationic polymer polyethylenimine (PEI) and free DNA. The application of each of these methods to different in vivo situations is presented: the use of DOGS for transfecting embryos and the developing mammalian nervous system; the recent application of PEI to the nervous system; and how naked DNA can be employed for transfecting different muscles and brain. The relative efficiencies are compared on the basis of luciferase reporter gene expression assessed in each tissue with the most appropriate vector system. Finally, the perspectives for constructing composite vectors combining safety and efficiency are considered briefly.