Several investigations have been reported on the interactive relation between the normal flora and the pathogenic micro-organisms in the human upper respiratory tracts (Thompson, Sanders, etc). It has also been known that some alpha-streptococci have inhibitory effect on the growth of group A beta-hemolytic streptococci. A study upon the role of alpha-streptococci in the throat (tonsil and pharynx) was performed using 73 culture specimens (throat swabs) obtained from 42 patients. Forty-four specimens were taken from the patients who received tonsillectomy, pre- and postoperatively, and 29 were from the patients who did not receive the operation. In the group of patients who received tonsillectomy, alpha-streptococci with inhibitory effect on the growth of group A beta-streptococci were detected less frequently preoperatively, when compared with the patients without tonsillectomy. On the other hand, postoperatively, marked increase of alpha-streptococci of these types was found in the normal flora of the throat. However, further detailed study on this subject is necessary because of the exceptional results in our observations.