The beta plasmid from Streptococcus faecalis strain DS5, which codes for resistance to erythromycin and lincomycin, was introduced into a Lancefield group F streptococcus, strain DR1501, by transformation. This strain, DR1501 (beta), was found to be an excellent donor of the beta plasmid and readily transferred the resistance markers to various lactic acid bacteria, including certain strains of S. mutans, S. sanguis, and S. salivarius. Evidence is presented indicating that the transfer of the beta plasmid is mediated by a mechanism that requires cell-to-cell contact. The transfer of plasmid DNA during conjugation has been confirmed by the isolation of beta plasmid from transconjugant clones and by their ability to then serve as donors of the erythromycin and lincomycin resistance markers.