Diþ erences between four avian species of commercial importance (chicken, turkey, duck and goose), in terms of the relationship between the dietary fatty acids supplied in the diet of the layers and the fatty acid composition of the egg yolk lipids, were investigated. Laying hens of the four species were provided with diets with very similar fatty acid compositions. The polyunsaturated fatty acid content of the diets consisted of linoleic and a-linolenic acids at approximately 50% and 6% (w/w of total fatty acids), respectively, for all four species. In spite of the very similar dietary provision of fatty acids, the subsequent fatty acid proüles of the yolk lipids diþ ered markedly between the four species. In particular, the proportion of docosahexaenoic acid in the total lipid of the yolk was three to üve times greater for the chicken compared to the other three species. By contrast, the proportion of arachidonic acid in total yolk lipid was approximately two times greater for the goose and duck than for the chicken and turkey. Thus the chicken was more efficient at incorporating long-chain (C 22 ) fatty acid of the n-3 series into yolk lipid whereas the duck and goose preferentially incorporated C 20 fatty acid of the n-6 series. The turkey eggs contained a similar proportion of arachidonic acid but less docosahexaenoic acid than the chicken eggs. The main diþ erences between the avian species in terms of the yolk levels of polyunsaturated fatty acids were in the phospholipid fraction since only low C 20h22 levels of these fatty acids were present in the triacylglycerol fraction. The relative proportions of docosahexaenoic acid in the phospholipid and triacylglycerol fractions of the livers of the newlyhatched chicks of the four species reýected the diþ erences displayed by the yolks. The proportions of arachidonic acid in these liver lipid fractions, however, did not reýect the species diþ erences in yolk lipid composition.