this paper presents the findings of a study in which throat cultures was ontained from all grade of primary school surrounding Seoul area. The number and percentages of children with positive throat cultures of streptococci were 181 cases (9.4%) among 1914 cases. Group A streptococci composed 4.3% (83 cases) of betahemolytic streptococci recovered. A total of 181 strains of group A streptococci were tested for susceptibility to 21 anibiotics in vitro. The strains were almost equally sensitive to most of the individual antibiotics : all of the group A strains were uniformly susceptible to bacitracin ; 93.6% to ampicillin ; 82.3% to erythromycin. The susceptibility to colymycin to colymycin and kanamycin were not found.