Dietary flax seed may prove to be a key feed ingredient in establishing the egg as a food useful for promoting cardiovascular health in humans. Yolk linolenic acid (LNA; 18:3n−3) increases in a linear fashion in response to graded levels of ground flax seed and whole flax seed if grit is provided in the feed to promote in vivo seed grinding. In contrast, the metabolic derivatives of LNA, eicosapentaenoic acid (EPA; 20:5n−3) and docosahexaenoic acid (DHA; 22:6n−3), are deposited only in limited amounts regardless of the level or form of flax seed fed. The distribution of the omega-3 polyunsaturated fatty acids (n−3 PUFA) in egg yolk lipid classes varies between laying stocks and these differences appear to influence the oxidative and sensory qualities of the product. Dietary flax seed results in apparently benign fluctuations in body weight of mature laying hens. Undesirable changes in egg production have only been reported for young birds early in their reproductive cycles. Changes in egg quality include reduced shell weight and decreased yolk weight. It is proposed that yolk weight reduction is related to changes in circulating oestradiol brought about by either n−3 PUFA or the phyto-oestrogens characteristic of flax seed.