The formation of long-chain (LC) polyunsaturated fatty acids (PUFAs)from the parent essential fatty acids (EFAs) in early life is limited, thusinfants are dependent on the exogenous provision of LC-PUFAs from humanmilk or supplemented formula. LC-PUFAs are structural components of alltissues, they are indispensable for cell membrane synthesis and for the functionof key organelles such as mitochondria, endoplasmic reticulum andsynaptic vesicles; and also for membrane receptors and signal transductionsystems. The brain, retina and other neural tissues are particularly rich inLC-PUFAs; if diet is deficient in LC-PUFAs during early life, neural structuraldevelopment and function are affected. LC-PUFAs also serve as specificprecursors for 20-carbon eicosanoid production (prostaglandins, prostacyclins,thromboxanes, and leukotrienes). Recently docosanoids derived from22-carbon LC-PUFAs have been identified and their capacity to protectneural tissue from hypoxia-reperfusion injury characterized. Eicosanoids anddocosanoids act as autocrine and paracrine mediators. They are powerfulregulators of numerous cell and tissue functions (e.g. thrombocyte aggregation,inflammatory reactions and leukocyte functions, cytokine release andaction, vasoconstriction and vasodilatation, blood pressure control, bronchialconstriction, and uterine contraction).