The present study investigated whether Helicobacter pylori water extract induces the upregulation of intercellular adhesion molecule-1, vascular cell adhesion molecule-1 and E-selectin on human umbilical vein endothelial cells, using an ELISA. The nature of the substances mediating this upregulation was also analyzed. H pylori water extract derived from type strain (NCTC 11637) significantly upregulated intercellular adhesion molecule-1, vascular cell adhesion molecule-1 and E-selectin to the same extent as interleukin-1. Treatments with extracts from clinical strains showed no significant increases in expression of these adhesion molecules. In a fractionation study, approximately 7 kDa fraction showed peak activity. This activity was tolerant to heating and trypsin digestion. These results indicate that H pylori water extract contains water-soluble, low-molecular, nonprotein substances which induce upregulation of adhesion molecules on human umbilical vein endothelial cells, suggesting that products of H pylori may elicit gastric mucosal inflammation by promoting expression of endothelial adhesion molecules.