Lactobacillus helveticus Lh59 produces a high-molecular-mass exopolysaccharide (> or = 2 x 10(6) Da) when cultured in skimmed milk. Compositional analysis, methylation analysis and NMR experiments (1H and 13C) recorded from the native polysaccharide as well as from oligosaccharides released by partial acid hydrolysis, allowed the complete structural determination of this polysaccharide, which consists of the following hexasaccharide repeating unit: [symbol: see text] This structure is identical to the one of an EPS produced by L. helveticus TN-4, which was claimed to be a spontaneous mutant of strain TY1-2.