A high-molecular-weight constituent of cranberry juice has been found to inhibit the sialyllactose specific adhesion of Helicobacter pylori strains to immobilized human mucus, erythrocytes, and cultured gastric epithelial cells. Different isolates of H. pylori differ in their affinity to the cranberry juice constituent. Cranberry juice may also inhibit adhesion of bacteria to the stomach in vivo, and may prove useful for the prevention of stomach ulcer that is caused by H. pylori.