The biological defence systems against oxygen radical toxicity and chemical toxicity, and their component enzymes, are described, and the nutritional requirements for biological defence against chemical and oxygen toxicity, including calories, protein, lipids and lipotropes, vitamins and minerals, are reviewed in the context of their contribution to the mechanisms of detoxication. Modulation of the cytochromes P-450, and hence toxicity, by dietary components are considered; the P450I family, induced by food pyrolysis mutagens, and the P450IIE family, induced by alcohol and fasting, contribute substantially to chemical toxicity and carcinogenicity. It is concluded that: (i) the detoxication system of terrestrial fauna has evolved over greater than 300 million years to protect animals from dietary plant toxins; (ii) protection against chemical and oxygen toxicity requires all categories of nutrients; and (iii) the rôle of food and nutrition in detoxication is essential to survival.