Abstract: The present invention discloses a method for treating Streptococcal infections of the upper respiratory tract, comprising administering an effective amount of a lysin enzyme produced by group C Streptococcal bacteria infected with a C1 bacteriophage specific for the bacteria to a mouth, throat, or nasal passage of a mammal, the method providing a concentration of from about 100 to 500,000 active enzyme units per milliliter of fluid in the environment of said nasal or oral passages.