Direct DNA transformation is currently the method of choice for obtaining transformed cereals, such as Zea mays , owing to the inherent host limitations of Agrobacterium tumefaciens . This soil bacterium, which naturally acts by transferring its own genes into a host plant, is commonly engineered for transferring foreign genes into plants, but its host range is limited mainly to dicots and noncereal monocots, and generally cannot be used to transfer foreign genes into maize (1 ,2 ). Among the methods for direct (Agrobacterium -independent) gene transfer, electroporation has proven to be an extremely efficient and general mechanism for introducing DNA, RNA, and other macromolecules into maize protoplasts (cells in which the cell wall is enzymatically removed prior to electroporation).