Teichoic acid (C polysaccharide) was extracted and purified from Streptococcus pneumoniae R6 with standard procedures except that lipoteichoic acid was extracted first. The dephosphorylated repeating unit was isolated after hydrolysis with 48% (by mass) HF, the bis(phosphocholine)-containing repeating unit was isolated by alkali hydrolysis, anion-exchange chromatography and phosphomonoester cleavage. On the basis of compositional analysis, fast-atom-bombardment mass spectrometry and NMR spectroscopy the following structure is proposed: [formula: see text] where AATGal is 2-acetamido-4-amino-2,4,6-trideoxy-D-galactose. The repeating units are linked to each other by phosphodiester bonds between O5 of the ribitol and O6 of the glucopyranosyl residue of adjacent units. This chain structure is identical with that previously established for pneumococcal lipoteichoic acid [Behr, T., Fischer, W., Peter-Katalinić, J. & Egge, H. (1992) Eur. J. Biochem. 207, 1063-1075]. This represents a unique situation because in other Gram-positive bacteria teichoic and lipoteichoic acids are structurally unrelated.