A range of potential chemoprotective agents, most of them natural dietary constituents, has been examined for ability to modulate both phase I (cytochrome P450 1A1, 1A2, 2B1/2, 2C11, 2E1, 3A, 4A) and phase II drug metabolizing enzymes (glutathione S-transferases, in particular subunits Yc2 and P,