We have undertaken a systematic study to test the transformation of various species of gram-negative bacteria using the electroporation method. The data obtained show very clearly that a great variety of gram-negative bacteria--15 different species belonging to 11 different genera--including freshly isolated wild-type strains can be transformed efficiently by use of the electric-field mediated transformation technique. These include species of the families Enterobacteriaceae, Pseudomonadaceae, Rhizobiaceae, photosynthetic bacteria and strains for which transformation could not be achieved, up to now, by other methods.