Modifiers of gastric carcinogenesis are reviewed with evidence of experimental results using rats. 1) Physical modifiers: Route of administration, medium (vehicle) of carcinogens, detergents, dosage (concentration), period (frequency) of administration, exposure time, and condition of mucus. Effects of surfactants and presence of a foreign body in the stomach lumen are also samples of physical enhancing factors. 2) Biological modifiers: Species, genetics, sex, hormonal factors, nutrition, and age. Moreover, effect of preexisting ulceration is important. 3) Chemical modifiers: Chemical substances administered prior to, simultaneously with, or following exposure of experimental animals to chemical carcinogens, or promoters of carcinogenesis. Chemical modifiers are: co-initiators, tumor promoters and inhibitors. NaCl having both co-initiator and tumor promoter action on MNNG gastric carcinogenesis is clearly shown in our investigations.