High frequencies of erythromycin-resistant streptococci were reported in Japan in the mid-1970s, and in Finland in the late 1980s, related to an increase in the consumption of macrolide antibiotics in these countries. The frequency of erythromycin-resistant Streptococcus pyogenes was reported to be only 2% in 1994, but we know that the susceptibility of the strains to antibiotics had not been tested routinely. We studied the resistance rates of Streptococcus pyogenes to various antibiotics in Seoul, Korea, where antibiotics could be purchased without prescription. From January through December, 1998, 92 isolates of group A streptococci were collected from inpatients and outpatients with pharyngotonsillitis or invasive streptococcal infections, from institutions in five different geographic areas of Seoul; one pediatric clinic, three university hospitals, and one general hospital. All isolates were serotyped by T-agglutination, and minimum inhibitory concentrations (MICs) were determined by agar dilution methods, according to the guidelines of the National Committee for Clinical Laboratory Standards (NCCLS). The most common T-serotype was T12 (44.6%), followed by T4 (19.6%). All the isolates tested were susceptible to penicillin, vancomycin, and cefotaxime. However, 38 isolates (41.3%) were resistant to erythromycin, 32 (34.8%) were resistant to clindamycin, and 48 (52.1%) were resistant to tetracycline. Twenty-seven of 41 isolates serotyped T12 and 3 of 18 isolates serotyped T28 were multiresistant to erythromycin, clindamycin, and tetracycline. Almost half of the isolates obtained from the five different areas in Seoul showed erythromycin resistance in Streptococcus pyogenes. Routine monitoring of antibiotic susceptibility tests and further extensive nationwide surveys are needed to determine the frequency and the extent of the spread of resistant strains in various geographic regions in Korea.