In order to develop a safe and effective way to introduce exogenous genes into cells, we have experimented with a new method of electroporation which uses a radio-frequency (RF) electric field to permeabilize the cell membrane. This RF method has several advantages over the conventional electroporation method which uses a direct current (DC) field. We have shown that the RF electroporation method can be used to introduce marker genes into a wide variety of cell lines, including COS-M6, CV-1, CHO, 3T3 and hepatocytes, and is able to increase substantially the efficiency of gene transfection. (For example, the amount of DNA required for transfecting two million COS-M6 cells can be as low as 0.1 microgram). The transfection efficiency is shown to be affected by a number of factors, including cell type, field strength, pulse protocol and medium buffer. Because of its wide range of applications, high transfection efficiency and lack of harmful side-effect, the RF electroporation method would be particularly useful for introducing genes into human cells for gene therapy.