The use of plasmid DNA to elicit immune responses has greatly increased our ability to skew the desired immune response to a particular antigen. DNA immunization elicits potent cell-mediated responses including humoral immunity as well as cytolytic T-lymphocyte immunity. This review will first discuss the overall immune response induced by naked DNA vaccination and will then summarize recent advances in basic research on DNA immunization, which have furthered our understanding of the role of DNA as an adjuvant as well as a carrier of genetic material. Subsequently, we will consider the possible mechanisms by which DNA immunization is able to induce such immune responses and how DNA immunization may be useful in both basic science research and also in future vaccine development in various disease processes. Finally, we will examine the advantages and disadvantages of DNA vaccines as well as safety issues. In conclusion, DNA vaccination shows promise in a number of areas including infectious diseases, allergy and cancer immunotherapies.