In the present study we investigated the macrolide-lincosamide-streptogramin B (MLSB) resistance in 47 clinical isolates of group C beta-hemolytic streptococci and 17 group G streptococci. Resistance to erythromycin was found in 31.6%; and 47%, respectively. On the basis of the erythromycin-clindamycin double-disk test, all strains were assigned to the MLSB phenotype. None of the strains were of the M phenotype. The distribution of the erythromycin-resistant genes were studied by dot blot hybridization and PCR. Resistance to erythromycin was due to the presence of mefA, ermB and ermTR genes. The ermTR gene was predominant among the group C and G streptococci (90% of the strains). Different mechanisms of erythromycin resistance predominate in group C and G streptococci than in Streptococcus pyogenes where there is an association between erythromycin resistance and active-efflux mechanism. Two of the strains harbored more than one erythromycin-resistant gene.