Gangliosides are glycosphingolipids that are widely distributed in vertebrate tissues and body fluids and which are specially abundant in neural tissues. Milk from different species has a particular ganglioside content and profile. Human milk has a higher content of gangliosides than bovine milk. GD3 and GM3 are the predominant individual gangliosides in bovine milk. In human colostrum GD3 is also the main ganglioside whereas in human mature milk GM3 predominates over the other gangliosides. Human milk also contains GM1 and a number of highly polar gangliosides, which may play an important role in infant physiology. GM1 has been shown to inhibit Escherichia coli and Vibrio cholerae enterotoxins. We have found that a ganglioside-supplemented infant formula modifies the intestinal ecology of preterm newborns, increasing the Bifidobacteria content and lowering that of Escherichia coli. Although the exact mechanism by which dietary gangliosides reduce the fecal content of Escherichia coli is unknown, in vitro experiments suggest that they may act as false intestinal receptors for some strains of this bacteria. Since GD3 and other gangliosides have been involved in mechanisms of lymphocyte activation and differentiation, dietary gangliosides might have a function in intestinal immunity development.