Group A streptococci (S. pyogenes) possess a number of capsule and cell wall associated components and release many extracellular proteins (toxins and hydrolytic enzymes) that are known or thought to contribute to the virulence and pathogenicity of the microorganism. Groupe A streptococci cause a wide array of infections, the most frequent of which are acute pharyngitis and pyoderma with two severe sequelae (acute rheumatic fever and glomerulonephritis). Other manifestations are scarlet fever and various soft tissue infections as well as sepsis and the recently characterized streptococcal toxic shock syndrome. The somatic components of group A streptococci include cell wall M protein, capsular hyaluronic acid, lipoteichoic acid, peptidoglycan, fibronectin binding protein, C5a peptidase and receptors for various human plasma proteins particularly IgA and IgG. The extracellular products are numerous and consist of among others the hemolytic toxins streptolysins S and O, hyaluronidase, streptokinase and cysteinyl proteinase as well as the superantigens erythrogenic toxins A and C also known as pyrogenic exotoxins.