Erythromycin is a macrolide antibiotic and inhibits bacterial protein synthesis by stimulating the dissociation of the peptidyl-tRNA molecule from the ribosomes during elongation. The use of macrolides has increased dramatically over the last few years and has led to an increase in bacterial resistance to these antibiotics. Bacterial resistance to erythromycin is generally conferred by the ribosome methylation and/or transport (efflux) protein genes. Among the identified erythromycin-resistant genes, erm(B) (erythromycin methylation) and mef(A) (macrolide efflux) are generally detectable in erythromycin-resistant streptococcal species. The distribution of these genes in oral streptococcal isolates has been reported in studies from other countries but has not been previously examined in a Korean study. We here examined by PCR the presence of erm(B) and mef(A) in oral streptococci isolated from Korean dental plaques. Among the 57 erythromycin-resistant strains tested, 64.9% harbored erm(B) whereas 40.4% were positive for mef(A). Eleven isolates had both the erm(B) and mef(A) genes. Twenty six isolates had only erm(B) and 12 isolates had only mef(A). Eight of the 57 strains examined were negative for both genes.