Experiments were performed to demonstrate that adherence of Helicobacter pylori to gastric epithelial cells causes alterations in the cell cytoskeleton. H. pylori intimately attached to cultured human gastric epithelial cells on small cellular projections, while there was no intimate association of H. pylori with cultured human esophageal epithelial cells. Fluorescein-conjugated phalloidin staining of gastric epithelial cells showed that H. pylori adherence stimulated actin polymerization; this stimulation was not observed with esophageal cells. Also, this organism's selectivity for gastric mucosa was supported by rare binding of bacteria to esophageal epithelial cells and gastric fibroblasts.