Electroporation, originally developed as a method to introduce DNA into eukaryotic cells (1 ), has subsequently been extensively used for bacterial transformation (2 ,3 ). This procedure is an effective method for the transfer of DNA to a wide range of Gram-negative bacteria, such as Escherichia coli , and reports indicate that 109 electro-transformants per microgram of DNA can be achieved in this species (4 ,5 ). Electroporation is probably the most efficient and reliable method for the transformation of E. coli strains using plasmid DNA.