Organochemical studies on food-derived mutagenic/carcinogenic components were described. Regulation of formation of carcinogenic nitrosamines in the reaction of secondary amines with nitrite under acidic conditions by food factors was described: stimulation by ethanol and suppression by unsaturated fatty acids and protein digests. Unique mutagenic diazo compounds produced in the reaction of monophenolics with nitrite generated carbon-centered radicals that bound to the base moieties of DNA molecules and caused DNA single strand breaks. The nitrate content in Japanese vegetables was high enough to produce nitrosamines in stomach. Nitric oxide generated in the body may produce nitrosamines and reactive oxygen species under neutral conditions. Mutagenic/carcinogenic heterocyclic amines were found in processed foods, smoked-dried bonito meat, roasted coffee beans and charred egg. Loss of water increased the mutagenicity of heated meats. Reduction of heterocyclic amines in cooked hamburger was successful by suppressing intermediary pyrazine cation radical in two ways: addition of an appropriate amount of sugar or onion, and addition of ascorbate or erythorbate. Food reductones, hydroxyfuranones in soy sauce and Maillard reaction mixtures and hydroxyhydroquinone in coffee, generated reactive oxygen species in vitro to cause DNA single strand breaks. The reductones induced minor DNA damage in vivo, but caused increased type I and IV allergy responses.