Abstract: The present invention is related to methods in which an electric field pulse is applied to cells and tissue. Several embodiments of the present invention relate to the application of electric field pulses to cells to regulate the physiology and biophysical properties of various cell types, including terminally differentiated and rapidly dividing cells. Methods of regulating transcription of a gene in a cell, marking a cell for diagnostic or therapeutic procedures, determining cellular tolerance to electroperturbation, selectively electroperturbing a population of cells, reducing proliferation of rapidly dividing cells in a patient, and facilitating entry of a diagnostic or therapeutic agent into a cell's intracellular structures are also provided.