In the past couple of years, the idea that naked DNA can be used to vaccinate against infections has been rapidly developing. In contrast to traditional protein or live attenuated vaccines, there is no risk of disease caused by DNA vaccines as only selected proteins are encoded. The ease with which DNA may be manipulated means that vaccines can be custom designed to meet many needs. In animal model systems, DNA vaccines have proved to be as effective as traditional vaccines. Additionally, this technology may also be used to control existing chronic infections. Possibilities for treating hepatitis B, herpes simplex virus-2 and HIV, as well as infections with parasites, are being explored with success.