Genetic vaccines have progressed significantly since the first demonstration of the technology in 1992. When Sanford and Johnston first developed the idea, two applications were envisaged. One was as a new, simple, possibly more effective, method for delivering vaccines. The other was as a new tool to explore the immune system and to discover new vaccines. As there has been relatively little emphasis on the latter, we provide three examples of the potential uses of genetic immunization for discovery/manipulation. One of these technologies may have important implications for the safety of the vaccines. Finally, we propose that the clinical application of genetic vaccines may be limited by inadequate delivery systems and propose the characteristics of an ideal system.