A transformation system for Enterococcusfaecalis was developed which uses untreated (i.e. non-protoplasted) cells and the electroporation technique. The optimized protocol resulted in transformation efficiencies of up to 4 × 106 transformants per μg of plasmid DNA. All strains of E. faecalis tested could be transformed by this method, albeit with differing transformation efficiencies. Using the protocol optimized for E. faecalis we successfully transformed Enterococcusfaecium, E. hirae, E. malodoratus and E. mundtii.