Breast milk oligosaccharides are excreted in urine in amounts that suggest that they may exist in the circulation at levels compatible with a physiological function. Some oligosaccharides have structural similarity to cellular adhesion molecules and may influence adhesion of cells in breast fed infants. In this study, breast milk oligosaccharides were purified and incubated in assays of cell adhesion. They were found to inhibit neutrophil adhesion to stimulated vascular endothelial cells in a dose dependent fashion. In contrast they enhanced platelet-neutrophil complex formation. These results indicate that breast milk oligosaccharides may play a physiological role in modulating cellular adhesion in vivo.