Since the discovery of streptococci by the surgeon of Vienna, Theodor Billroth, more than 100 years ago, they have proved to be a bacterial group of great medical and epidemiological importance. The classification in growth-characteristics on blood culture mediums (alpha-, beta- and gamma-hemolysis) has been detached by the evidence of group specific cell wall antigens. The antigene extraction described by Lancefield can distinguish at least 21 serogroups (A-T). They have also taken over the historical names (S. pyogenes, S. agalactiae etc.). In addition to group relationship the antigen structure of the streptococci cell wall (carbohydrates, peptidoglycanes, M-T-R-proteins and others) is responsible for antigenetic and pathogenetic conditions. Some species of streptococci do also excrete exotoxines (streptolysin, hyaluronidase, bacteriocines, erythrogenic toxins) with antigenetic and pathogenetic significance. Infections with streptococci of the serogroup A, B, D and H are numerously and medically significant. There is a great interest in infections due to A streptococci (pharygitis, impetigo, erysipel, scarlatin fever). The known non-purulent diseases following A streptococci infections (acute rheumatoid fever, acute glomerulonephritis) are streptococcal specific reactions for the individual. Some antigens of the cell wall and also some exotoxines react in human beings as autoantigenes. Human beings are the most important reservoir for streptococci. Nearly 20% of a population have A streptococci in their upper respiratory tract.(ABSTRACT TRUNCATED AT 250 WORDS)