This paper describes a serological method for differentiating hemolytic streptococci into several groups based on precipitin reactions. The study involved 106 strains of Streptococcus haemolyticus isolated from various sources, including humans, animals, and dairy products. The classification is based on the presence of a specific carbohydrate, the C substance, which is not type-specific but is characteristic of human strains. The results show that strains can be grouped into five distinct categories: Group A (human origin), Group B (bovine and dairy sources), Group C (lower animals), Group D (cheese), and Group E (certified milk). The serological test provides a reliable means of identifying the probable origin of a strain, which is more accurate than biochemical and cultural methods. The precipitin test is more effective than the agglutination reaction because it reveals specific groupings that are not detected by agglutination. The study also highlights the importance of the C substance in distinguishing human strains from those of animal origin. The results confirm that the serological method is a valuable tool for classifying hemolytic streptococci and provides a basis for further research into their epidemiological significance.This paper describes a serological method for differentiating hemolytic streptococci into several groups based on precipitin reactions. The study involved 106 strains of Streptococcus haemolyticus isolated from various sources, including humans, animals, and dairy products. The classification is based on the presence of a specific carbohydrate, the C substance, which is not type-specific but is characteristic of human strains. The results show that strains can be grouped into five distinct categories: Group A (human origin), Group B (bovine and dairy sources), Group C (lower animals), Group D (cheese), and Group E (certified milk). The serological test provides a reliable means of identifying the probable origin of a strain, which is more accurate than biochemical and cultural methods. The precipitin test is more effective than the agglutination reaction because it reveals specific groupings that are not detected by agglutination. The study also highlights the importance of the C substance in distinguishing human strains from those of animal origin. The results confirm that the serological method is a valuable tool for classifying hemolytic streptococci and provides a basis for further research into their epidemiological significance.