Itisonlyrecently thatthe naturaloccurrenceoffree radicalsin biological tissue has become widely accepted, and that the suspi- cion with which biologists previously viewed the free radicals of radiationchemistryhas beenplacedin a broaderperspective. Now, oxygen-derived free radicals are considered respectable biochemi- cal intermediates, given always the caveat that unwanted tissue damage may arise if these active species are produced in such abundance that they overwhelm the natural antioxidant and free- radical defense mechanisms, or if these systems have become hypoeffective. Many factors, including several dietary manipula- tions, can lead toelevatedproductionofsuperoxide and may result in free radical overload, whereas a deficiency of those micronutri- ents associated with the antioxidant defense mec.hanisms may re- sult in substantially diminished antioxidant capacity. By now, antioxidants have become a household word and al- most everyone is aware of their imponance in protecting the body against attack by active oxygen species. Indeed, it is a paradox of nature that oxygen, which is so essential to sustain aerobic life, ul- timately contributes to its destruction. Not surprisingly, recogni- tion ofthis dilemma has generated a spate ofantioxidant strategies intended to reduce the risk of tissue damage by rampant oxygen radicals, some sadly based less on science than on speculation.

F. Macfarlane Burnet I have been an interested onlooker for many years at research on the biology of trace elements, particularly in its bearing on the pas toral and agricultural importance of copper, zinc, cobalt, and mo lybdenum deficiencies in the soil of various parts of Australia. More recently I have developed a rather more specific interest in the role of zinc, particularly in relation to the dominance of zinc metalloenzymes in the processes of DNA replication and repair, and its possible significance for human pathology. One area of special significance is the striking effect of zinc deficiency in the mother in producing congenital abnormalities in the fetus. The fact that several chapters in the present work are concerned with this and other aspects of zinc deficiency is, I fancy, the editors jus tification for inviting me to write this foreword. In reading several of the chpaters before publication, my main impression was of the great potential importance of the topic of trace metal biology in both its negative and positive aspects-the effects of deficiency of essential elements and the toxicity of such pollutants of the modern world as lead or mercury mainly as or ganic compounds."

This text is a treatise drawing together and critically examining the current explosion of experimental and clinical research on the metabolism, nutrition, pharmacology, toxicology, pathology, neuropsychology, and developmental neurobiology of trace elements.

F. Macfarlane Burnet I have been an interested onlooker for many years at research on the biology of trace elements, particularly in its bearing on the pas toral and agricultural importance of copper, zinc, cobalt, and mo lybdenum deficiencies in the soil of various parts of Australia. More recently I have developed a rather more specific interest in the role of zinc, particularly in relation to the dominance of zinc metalloenzymes in the processes of DNA replication and repair, and its possible significance for human pathology. One area of special significance is the striking effect of zinc deficiency in the mother in producing congenital abnormalities in the fetus. The fact that several chapters in the present work are concerned with this and other aspects of zinc deficiency is, I fancy, the editors jus tification for inviting me to write this foreword. In reading several of the chpaters before publication, my main impression was of the great potential importance of the topic of trace metal biology in both its negative and positive aspects-the effects of deficiency of essential elements and the toxicity of such pollutants of the modern world as lead or mercury mainly as or ganic compounds.

Itisonlyrecently thatthe naturaloccurrenceoffree radicalsin biological tissue has become widely accepted, and that the suspi- cion with which biologists previously viewed the free radicals of radiationchemistryhas beenplacedin a broaderperspective. Now, oxygen-derived free radicals are considered respectable biochemi- cal intermediates, given always the caveat that unwanted tissue damage may arise if these active species are produced in such abundance that they overwhelm the natural antioxidant and free- radical defense mechanisms, or if these systems have become hypoeffective. Many factors, including several dietary manipula- tions, can lead toelevatedproductionofsuperoxide and may result in free radical overload, whereas a deficiency of those micronutri- ents associated with the antioxidant defense mec.hanisms may re- sult in substantially diminished antioxidant capacity. By now, antioxidants have become a household word and al- most everyone is aware of their imponance in protecting the body against attack by active oxygen species. Indeed, it is a paradox of nature that oxygen, which is so essential to sustain aerobic life, ul- timately contributes to its destruction. Not surprisingly, recogni- tion ofthis dilemma has generated a spate ofantioxidant strategies intended to reduce the risk of tissue damage by rampant oxygen radicals, some sadly based less on science than on speculation.