Determination of T-serotype for a total 245 strains (157 strains in 1986, 88 strains in 1987) of Streptococcus pyogenes (Group A hemolytic streptococci) isolated from clinical specimens (throat swab) of pediatric patients in Fukuoka Prefecture from 1986 until 1987 were performed. The susceptibilities of 9 antibiotics against 241 strains were studied. The most dominant strain was T-12 (57 strains, 36.3%) and followed by T-4 (32 strains, 20.4%) and T-28 (30 strains, 19.1%) in 1986. The total of these three strains was 75.8% of all strains. In 1987, T-4 (41 strains, 46.6%) was the dominant strain instead of T-12 (14 strains, 15.9%). T-28 was isolated only 4 strains (4.5%) in 1987, although it was isolated in 30 stains (19.1%) in 1986. In susceptibility-tests, no strains of 1986 and 1987 was resistant to beta-lactams. Resistant strains (MIC greater than or equal to 25 micrograms/ml) to erythromycin (EM), tetracycline (TC) and chloramphenicol (CP) were 4 (2.6%), 51 (33.3%) and 1 (0.7%), respectively in 1986. In 1987, resistant strains to EM and CP were not detected, to TC were 52 strains (59.1%), so there was an increase of susceptibility to EM and CP. As for relationship between T-serotype and antibiotic resistance, only one strain (T-12) showed multiple resistance in 1986, however in 1987, multiple resistant strain was not detected. In 1986 and 1987, 31 of 49 only TC resistant strains (63.3%) and 41 of 52 only TC resistant strains (78.8%) were T-4, respectively.