Mass immunization against bioterrorism or other public health threats will require reagents and devices that are simple, effective, reproducible, and inexpensive. DNA vaccines fit most of these criteria, but the safe and efficient delivery of exogenous DNA to cells in vivo is an obstacle that will need to be surmounted. Gene electrotransfer is a powerful method that can achieve long-lasting gene expression in different tissue types of various species; transfection efficiency by electroporation is also much greater than that of DNA injection. In traditional clinical electroporation devices, a great deal of current must be passed to generate a sufficient voltage field for electroporation to occur, risking tissue damage. Other devices make use of needles that employ open-loop circuitry in delivering the voltage to the tissue. Accordingly, voltage levels are set very high, which can cause significant tissue damage. Moreover, during the course of electroporation, the resistance of the tissue that is being stimulated changes, meaning a new current is required to maintain a constant voltage field. Without repeated assessment of the resistance of tissue to ensure appropriate current compensation, the efficiency of electroporation will decrease during the stimulation process.