The streptococci represent a diverse group of Gram-positive bacteria that includes both medically and industrially important members. Many species elaborate capsular polysaccharides, while others may produce extracellular polysaccharides that do not form distinct capsules. Studies of capsular polysaccharides of the streptococci have been central to the advancement of genetics, pathogenesis, and immunology. Griffith’s 1928 description of the transformation of pneumococcal capsular polysaccharides in the mouse was the first observation of a mechanism of bacterial gene transfer. 1 Attempts to define the “transforming principle” ultimately led Avery, MacLeod, and McCarty to identify DNA as the hereditary material. 2 Other classic studies with S. pneumoniae demonstrated the essential nature of the capsule in virulence, antiphagocytosis, and immunity. 3-6 Its significance is further reflected in the fact that virulence properties of the organism, including infectivity in animals and the ability to resist phagocytosis, are related in part to the specific capsular polysaccharide that is produced (see Kelly et al. [Reference 7] and references therein). Likewise, invasive neonatal infections due to Streptococcus agalactiae (group B streptococci) are predominantly caused by strains representing a single capsular serotype (III), 8 and encapsulated strains of Streptococcus pyogenes (group A streptococci) occur more frequently among isolates obtained from invasive and acute rheumatic fever infections than from uncomplicated pharyngitis. 9 In the industrially important Streptococcus thermophilus and Lactococcus lactis, synthesis of an exopolysaccharide is critical for enhancing the texture of fermented milk products.