The absorption and metabolism of allicin and allicin-derived compounds are only partially understood (5). Although a number of biological activities have been attributed to various allicin-derived compounds, it is not yet clear which of these compounds or metabolites actually reach target tissues (1). Animal studies using radiolabeled compounds indicate that allicin or its breakdown products are absorbed intestinally (6, 7). However, allicin and allicin-derived compounds, including diallylsufides, ajoene, and vinyldithiins, have never been detected in human blood, urine, or stool, even after the consumption of up to 25 g of fresh garlic or 60 mg of pure allicin (1). These findings suggest that allicin and allicin-derived compounds are rapidly metabolized. The concentration of allyl methyl sulfide in the breath has been proposed as an indicator of the bioavailability of allicin and allicin-derived compounds (5). Human consumption of crushed garlic and equivalent amounts of allicin, DATS, DADS, ajoene, and allyl methyl sulfide resulted in similar increases in breath concentrations of allyl methyl sulfide, suggesting that allicin and allicin-derived compounds are metabolized to allyl methyl sulfide, a volatile compound that can be measured in exhaled air.