Recent reports have indicated a high incidence of erythromycin resistance in Group A streptococci isolated from children in Japan. The present study investigated antibiotic susceptibility patterns of 280 pharyngeal isolates from ambulatory patients using the plate dilution technique. The incidences of resistance to erythromycin and tetracycline were 4.3 and 7.8%, respectively. No resistance to penicillin, ampicillin, methicillin, oxacillin, cefaclor or moxalactam was found, and there was no evidence of penicillin tolerance using the standard tube dilution technique. The erythromycin-resistant isolates were of T-pattern 12, M-type 12, and two erythromycin-resistant isolates were also resistant to tetracycline. Data on the source of the isolates suggest that a localized outbreak of erythromycin-resistant streptococcal infection occurred.