Improved devices and methods for performing electroporation-mediated delivery agents to cells is described. The method includes positioning a first electrode and a second electrode such that an electrical signal passed between the first electrode and the second electrode passes through the cell. The method also includes passing an electrical signal between the first electrode and the second electrode, the electrical signal having a frequency greater than about 10 kHz. In one embodiment of the method, the electrical signal has a bipolar waveform. In another embodiment of the method, the electrodes are positioned at a treatment site, e.g., a tumor, for in vivo delivery of an agent.