The present study was carried out to investigate the possibility that lipopolysaccharide deprived from Helicobacter pylori may alter gastric motility. To address the question, we examined the effect of H. pylori lipopolysaccharide on gastric emptying in conscious rats. Gastric emptying was evaluated by the phenol red method. Time-course and dose-related effects of intraperitoneal administration of H. pylori lipopolysaccharide were investigated. Intraperitoneal injection of H. pylori lipopolysaccharide significantly suppressed gastric emptying of a liquid meal in a dose-dependent manner. The inhibitory action of H. pylori lipopolysaccharide was observed 2, 4, 8, or 12 hr after the injection. These results suggest for the first time that H. pylori lipopolysaccharide may suppress gastric emptying in a long-lasting fashion. It is also suggested that H. pylori may influence gastric function through its cell wall structure named lipopolysaccharide.