A procedure to transform intact Lactobacillus sake cells by electroporation was developed through a systematic examination of the effect of changes in various parameters on the transformation efficiency of Lact. sake strain 64F. The most critical factors were found to be the electrical parameters, the composition of washing and electroporation/storage solutions, and the presence of MgCI2 in the expression medium. Under optimal conditions transformation efficiencies up to 107 transformants (μg supercoiled DNA)-1 were obtained. The optimized procedure was successfully applied to other Lact. sake strains and consistently yielded from 104 to 107 transformants (μg supercoiled DNA)-1.