More than 60% of all strains of group A streptococci isolated during the period from 1974 to 1975 from children with streptococcal infections in Hokkaido district, Japan, were highly resistant to erythromycin. These strains were found to be multiply resistant to lincomycin hydrochloride monohydrate, chloramphenicol, and tetracycline, and were exclusively type 12 by T-protein typing. The clinical symptoms produced by these organisms were rather mild, responded to penicillin well, and were rarely complicated with glomerulonephritis. The high prevalence of resistant group A streptococci was nationwide, which may have been related to recent excessive use of erythromycin and other macrolide antibiotics. Erythromycin can no longer be considered the drug of choice in the management of streptococcal infections in Japan. This suggests that a periodic surveillance of antibiotic sensitivity of streptococcal isolates may be necessary in other countries in which macrolide antibiotics are frequently prescribed.