Strains of Streptococcus pyogenes isolated from pediatric patients with acute infections which were resistant to one or more of the antibiotics, tetracycline (TC), chloramphenicol (CP), macrolide antibiotics (erythromycin, kitasamycin, oleandomycin, josamycin), lincomycin (LCM) and clindamycin (CLM), were used for transduction of drug resistance. These drug-resistant strains were treated with mitomycin C to induce phages and transduction of drug resistance was attempted by means of phages so induced. It was found that transduction of resistance to the above antibiotics was possible. The transductants obtained on TC-containing selective agar plate were resistant to TC alone while those produced on CP- or erythromycin (EM)-containing selective agar plate were resistant to CP, macrolide antibiotics (Mac), LCM and CLM. From this finding, it was inferred that transduction of resistance to TC, CP, Mac, LCM and CLM via phages occurred in two different patterns, i. e., transfer of resistance to TC alone and that of resistance to CP, Mac, LCM and CLM. All of the transductants obtained were found to belong to group A. In T-typing, they were of the same T-12 type as the donor and recipient strains in a majority of cases though some were not typable.