This study evaluated the antimicrobial susceptibilities and macrolide resistance mechanisms of β-hemolytic streptococci (BHS), and an additional objective was to assess the effects of 'the separation of prescribing and dispensing (SPD) of medications' on bacterial resistance rate and distribution of phenotypes and genotypes of erythromycin-resistant BHS by comparing the antimicrobial susceptibility data before (1990-2000) and after the implementation of SPD at one tertiary care hospital in South Korea. Between the period of January 2001 and December 2002, the minimal inhibitory concentrations of six antimicrobials were determined for 249 clinical isolates of BHS. Resistance mechanisms of erythromycin-resistant (intermediate and resistant) isolates were studied by using the double disk test and PCR. Overall, the resistance rates to tetracycline, erythromycin, and clindamycin were 75.5%, 32.9%, and 32.5%, respectively. Sixty-seven (81.7%) of 82 erythromycin-resistant isolates expressed constitutive resistance to macrolide-lincosamide-streptogramin B antibiotics (a constitutive MLS_B phenotype) ; 11 isolates (13.4%) expressed an M phenotype; and four isolates (4.9%) had an inducible MLS_B resistance phenotype. erm(A) was found in isolates with constitutive/inducible MLS_B phenotypes, erm(B) with the constitutive/inducible MLS_B phenotype, and mef(A) with the M phenotype. We found that resistance rates to erythromycin and clindamycin among S. agalactiae, S. pyogenes, and group C streptococci isolates were still high after the implementation of the SPD policy in Korea, and that the constitutive MLS_B resistance phenotype was dominant among erythromycin-resistant BHS in this Korean hospital.