There has been increasing interest on organic isothiocyanates especially on phenethylisothiocyanate (PEITC) as chemoprotective agents against several types of chemically induced tumors (Hecht 1995). These isothiocyanates are present in several cruciferous edible plants as complex thioglucosides called glucosinolates (Fenwick et al., 1983). They are released from the glucosinolates by the action of the hydrolytic enzyme myrosinase (thioglucoside glucohydrolase EC 3.2.3.1) which is present as several isoenzymes in the same plants and is released from the plants when the cells are crushed like in mastication. PEITC is found as its glucosinolate gluconasturtin in e.g. cabbage, broccoli, cauliflower and watercress, which are widely consumed as food. The chemoprotective action of isothiocyanates against carcinogens is thought to be due to their inhibitory effects against several Phase I detoxifying enzymes (cytochrome P-450s) which activate procar-cinogens and their induction of Phase II detoxifying enzymes like glutathione S-trans-ferase and quinone reductase (Zhang and Talalay, 1994) which aid in their excretion.