Allyl sulfides are bioactive phytochemicals found in garlic, onion, and other members of the genus Allium. Here we showed that diallyl disulfide and diallyl trisulfide can transfer allyl side chains to low molecular weight thiols. Diallyl monosulfide is inert with respect to this allyl transfer reaction. On the other hand, diallyl sulfone, a known metabolite of diallyl monosulfide, alkylates both amines and thiols under physiologically relevant conditions via isomerization to an electrophilic vinyl sulfone.