Eight species of bifidobacteria were tested for their abilities to grow on a range of monosaccharides (glucose, arabinose, xylose, galactose and mannose). In contrast to the other sugars, glucose and galactose were utilized by all species and, in general, specific growth rates were highest on these sugars. Different substrate preferences were observed between species when the bacteria were grown in the presence of all five monosaccharides. For example, glucose and xylose were co-utilized by Bifidobacterium longum, whereas glucose repressed uptake of all other sugars in B. bifidum and B. catenulatum. Galactose was the preferred substrate with B. pseudolongum. In B. angulatum, glucose and galactose were utilized simultaneously. B. breve did not grow on arabinose when this sugar provided the sole source of energy. However, glucose and arabinose were preferentially taken up during growth on sugar mixtures.