Over the past few years, intramuscular injection of non-replicating DNA expression vectors has been demonstrated to be generally applicable as an effective method of producing functional proteins in vivo. This technique has been useful in the study of growth factors, regulation of protein expression, transplantation rejection, gene therapy, immune regulation and the production of monoclonal antibodies. The most successful application of DNA injection has, however, been the generation of immune responses in animal models, with the ultimate goal of developing vaccines for humans. Therefore, this approach has the potential to be a new vaccine technology, in addition to its utility in other areas of research.