The first research that focused on the effects of pulsed electric fields on living cells described the phenomena of reversible and irreversible membrane breakdown in an in vitro environment in the 1960s and 1970s (1 –6 ). This early research led to the current understanding that exposing cells to intense electric fields induces a transmembrane potential that is superposed on the resting potential. Induced potentials of sufficient magnitude cause a dielectric breakdown of the membrane. This physical phenomenon was termed electroporation, or electropermeabilization, because it was observed that molecules that do not normally pass through the membrane gain intracellular access after the cells were treated with electric fields.