Proteins can be introduced into cells in several ways, including permeabilization by Sendai virus, trypsinization, osmotic shock, microinjection, electroporation, or after transfection of cells with expression vectors containing the gene(s) of interest. Unlike most of these other methods, electroporation is a simple, relatively inexpensive, and efficient method for rapidly introducing DNA, small molecules, and proteins into bacterial or mammalian cells (1–10). Electroporation has the advantage over other techniques in that many cells can be treated simultaneously and one or more compounds or macromolecules, such as proteins, can be introduced into cells at the same time (see Note 1).