An extracellular bacteriocin of Staphylococcus epidermidis isolated from dental plaque was purified and characterized. Its molecular mass was 3500 Da and pI was 10.5. This bacteriocin inhibited the growth of Staphylococcus aureus, Streptococcus salivarius, and Streptococcus mitis, but Streptococcus mutans, Streptococcus sanguis and other oral indigenous bacterial species examined were not inhibited. The mode of inhibition was found to be bacteriostatic.