The health benefits of garlic, including inhibition of carcinogenesis, are supported by several epidemiologic and laboratory findings. Garlic's sulfur components have been reported to suppress experimentally induced tumor incidence in several organs, including the colon. Studies in humans also suggest that dietary garlic constituents reduce the risk of colorectal adenomatous polyps, which are considered precursors to colon cancer. Aberrant crypt foci (ACF) are proposed to be early preneoplastic lesions of adenoma-carcinoma in humans and chemically induced colon cancer in rodents. In preclinical studies, both water- and lipid-soluble allyl sulfur compounds arising from processed garlic inhibited ACF. The response to these allyl sulfur compounds appears to depend on several factors, including the speciation, quantity, and duration provided.