We investigated cellular signaling and pepsinogen secretion in the human gastric adenocarcinoma cell line AGS which was pretreated with the purified vacuolating cytotoxin from Helicobacter pylori. Results indicated that vacuolating toxin increased the levels of inositol phosphates, cytosolic free calcium concentration, adenosine 3',5'-cyclic monophosphate, and phosphorylation of 31 kDa and 22 kDa proteins in the host cells. Moreover, pepsinogen secretion from AGS cells was stimulated with increasing concentrations of cytotoxin. We conclude that besides the H. pylori cytotoxin-induced cellular vacuoles, cytotoxin-stimulated signaling mediators and pepsinogen release are important factors involved in the etiology of chronic active gastritis and peptic ulcer disease.