Extensive evidence points to the ability of allyl sulfides from garlic to suppress tumor proliferation both in vitro and in vivo. This antineoplastic effect is generally greater for lipid-soluble than water-soluble allyl sulfides. Both concentration and duration of exposure can increase the antiproliferative effects of lipid- and water-soluble allyl sulfides. Part of their antiproliferative effects may relate to an increase in membrane fluidity and a suppression of integrin glycoprotein IIb-IIIa mediated adhesion. Alterations in cholesterol, arachidonic acid, phospholipids and/or thiols may account for these changes in membrane function. Allyl sulfides are also recognized for their ability to suppress cellular proliferation by blocking cells in the G2/M phase and by the induction of apoptosis. This increase in the G2/M and apoptotic cell populations correlates with depressed p34cdc2 kinase activity, increased histone acetylation, increased intracellular calcium and elevated cellular peroxide production. While impressive pre-clinical data exist about the antineoplastic effects of allyl sulfur compounds, considerably more attention needs to be given to their effects in humans. The composition of the entire diet and a host of genetic/epigenetic factors will likely determine the true benefits that might arise from allyl sulfur compounds from garlic and other Allium foods.