A high intake of cruciferous vegetables is associated with a reduced risk of cancer, particularly lung and those of the gastrointestinal tract. This protective effect has been linked to the presence of glucosinolates in these vegetables. Certain metabolites of the glucosinolates, particularly the isothiocyanates and nitriles have been shown to both modify xenobiotic metabolising enzymes and induce cell cycle arrest and apoptosis. Different metabolites are more or less effective in mediating each response depending on the model system employed. It is likely that a combination of these responses explains the chemo-preventive characteristics of Brassicas and that a combination of different cruciferous vegetables will provide optimal protection.