Overall, several investigations indicate that garlic and its organic allyl sulfur components inhibit the cancer process. Furthermore, these studies reveal that the benefits of garlic are not limited to a specific species, a particular tissue, or a specific carcinogen. Finally, odor is not a prerequisite for the protection provided by garlic against the initiation of chemical carcinogenesis. Although the water-soluble compound S-allyl cysteine is effective in reducing the risk of chemically induced tumors in experimental animals, it has no effect on established tumors. However, oil-soluble compounds such as diallyl disulfide are effective in reducing the proliferation of neoplasms. Although the evidence supports the benefits of garlic, additional evidence is needed to determine the quantity needed by humans to minimize cancer risk.