The lipoteichoic acid of Streptococcus lactis Kiel 42172 was isolated. The lipid portions were released by HF and were established to be 3-O-[O-alpha-D-galactopyranosyl-(1 leads to 6)-alpha-D-galactopyranosyl]-2-O-alpha-D-galactopyranosyl-sn-glycero-1-phosphate, they are joined by phosphodiester bonds nosyl)]glycerol. The repeating units of the hydrophilic chain were established to be 3-O-[O-alpha-D-galactopyranosyl-(1 leads to 6)-alpha-D-galactopyranosyl]-2-O-alpha-D-galactopyranosyl-sn-glycero-1-phosphate; they are joined by phosphodiester bonds at carbon atom 6 of the galabiosyl residues. The innermost unit is linked to the glycolipid by a phosphodiester presumably at C-6 of the outer glucosyl moiety. The hydrophilic chain is 7.4--11.8 units in length, measuring 12--19 nm is extended conformation. The content of 2.7--2.96 acyl groups per 2 glucosyl residues indicates that 70--96% of the glycolipid consists of acyldiglucosyldiacylglycerol. The novel poly(glycosylgly-cerophosphate) structure provided for the first time the oplipoteichoic acids are the sn-1 isomer which has previously been suggested from biosynthetic studies (Glaser, L., & Lindsay, B. (1974) Biochem. Biophys. Res. Commun. 59, 1131--1136).