In previous studies we found that immunizing mice with a somicate of Helicobacter felis and adjuvant cholera toxin (CT; 10 ug) protected the animals against challenge with viable H. felis. The aim of this study was to determine whether a low dose of CT or its nontoxic B subunit (CTB) was effective as an adjuvant in Helicobacter oral vaceines. Significant protection against viable H. felis challenge was achieved in the amimals immunized with H. felis antigen plus the combination fo 0.5ug fo CT and 10ug fo CTB (96%), with H. felis antigen plus 0.5ug of CT (95)%, and with H. felis antigen plus 10 ug of CTB (83%), No protective effect was found in the mice immunized with either H. fells antigen alone or adjuvant CTB and CT alone. Twenty-six percent fo mice immunized with Helicobacter pylori antigen plus CT (10ug) were protected against H. fells challenge, comfimning the value of the model in predicting effects of immunization im humans. The observation that immunity can be induced with a montoxic adjuvant CTB opens the wsy for human studies with H. pylori waceines and is a further step along the road to effective strategies of prevention fo gastroduodenat diseases of major wirld signififcaace.