Polyunsaturated fatty acids(PUFA) are vitally important for normal neonatal development. As well as providing a source of energy they are intrinsically involved in the establishment and maintenance of cell membrane structure and function. High PUFA levels, however, are subject to peroxidation and consequently require to be protected against free radical attack via an adequate antioxidant supply. The avian embryo was used as a model system as it is particularly dependent on PUFA and poor hatchability has recently been linked to inadequate PUFA metabolism. The micronutrient elements Se, Cu, Zn, Fe and Mn are involved in the antioxidant complex through their presence in the enzymes glutathione peroxidase (GSH-PX), superoxide dismutases (SOD) and catalase. The concentrations of these elements were measured in eggs and in chick embryonic and post hatch brains at different stages of development in order to elucidate their roles in the maintenance of PUFA metabolism.