Electroporation is a process in which a controlled electrical pulse is applied to cells, inducing a transient destabilization of the cell membrane. During this time, the cells are highly permeable to exogenous substances in the surrounding media. DNA, proteins, and small molecules are all taken up by cells during electroporation; introduction of DNA into cells is the most common application. Gene transfer by electroporation offers many advantages for analysis of gene expression. The technique is simple, rapid, and reproducible. It is especially suited to suspension cultures and certain cell types that are poorly trans-fected by other means. Because all cells are transfected instantaneously, and essentially simultaneously, it is particularly suited to quantitation of gene transfer. Finally, single-copy, stable transfectants can often be isolated (1 ). Whereas the basic mechanisms of electroporation are still largely unknown, optimizing the conditions for electroporation of any particular cell type is primarily empirical.