text: Gastric cancer is the major cancer in the developing world and one of the top two worldwide. Helicobacter pylori is a bacterium implicated in the etiology of stomach cancer. The incidence of stomach cancer is lower in individuals and populations with high Allium vegetable intakes. Allium vegetables, particularly garlic, have antibiotic activity. Standard antibiotic regimens against H. pylori are frequently ineffective in high-risk populations. As part of our study of the role of Allium vegetable intake on cancer prevention, we wished to investigate its antimicrobial activity against H. pylori. An aqueous extract of garlic cloves was standardized for its thiosulfinate concentration and tested for its antimicrobial activity on H. pylori grown on chocolate agar plates. Minimum inhibitory concentration was 40 micrograms thiosulfinate per milliliter. Staphylococcus aureus tested under the same conditions was not susceptible to garlic extract up to the maximum thiosulfinate concentration tested (160 micrograms/ml). To our knowledge, this is the first report of H. pylori's susceptibility to garlic extract of known thiosulfinate concentration. It is plausible that the sensitivity of H. pylori to garlic extract at such low concentration may be related to the reported lower risk of stomach cancer in those with a high Allium vegetable intake. Furthermore, it may identify a strategy for a low-cost intervention, with few side effects, in populations at high risk for stomach cancer, particularly where antibiotic resistance and the risk of reinfection are high.