The exopolysaccharides produced by Lactobacillus delbrueckii subsp, bulgaricus NCFB 2772 grown in defined medium were investigated, At equal cell densities, the strain produced 95 mg l(-1) exopolysaccharides with glucose and 30 mg l(-1) with fructose as the carbohydrate source. High-performance size-exclusion chromatography of the exopolysaccharides produced on glucose showed the presence of two fractions with relative molecular masses (M-r) of 1.7 x 10(6) and 4 x 10(4) in almost equal amounts, The exopolysaccharides produced on fructose contained mainly a fraction of low M-r of 4 x 10(4). The high-M-r fraction of the purified exopolysaccharides produced on glucose appeared to have a sugar composition of galactose, glucose and rhamnose in the molar ratio of 5:1:1, whereas the low-M-r weight fraction contained galactose, glucose and rhamnose in the molar ratio of approximately 11:1:0.3. The purified exopolysaccharide fractions produced on fructose showed comparable ratios, The high-molecular-mass fractions contained terminally linked galactose, 1,2,3-linked galactose, 1,3,3-linked galactose, 1,3-linked glucose and terminally linked rhamnose, The low-molecular-mass fractions contained mainly 1,3-linked galactose and 1,6-linked galactose and lower amounts of other sugar linkages, The production of the high-M-r fractions appeared to be dependent on the carbohydrate source, whereas the low-M-r fractions were produced more continuously.