1. The nutrient content of battery, deep litter and free range eggs from domestic hens under systems of management typical of those used in the commercial production of eggs was studied from January to March 1968.
2. Monthly samples of eighteen eggs, supplied by six centres, were homogenized, freezedried, ground and stored at −15°. Their contents of moisture, nitrogen, amino acids, fats, fatty acids and cholesterol, ash, sodium, potassium, calcium and iron, thiamin, riboflavin, nicotinic acid, pantothenic acid, folic acid, vitamin B12, tocopherols and retinol were determined. The mean values for eggs from each system, each centre and each quarter of the year were calculated.
3. For many nutrients, no significant difference between systems was detected; the greatest variations occurred in the content of some vitamins. Free range eggs contained more vitamin B12 than deep litter or battery eggs and more folic acid (Lactobacillus casei assay) than battery eggs. Differences in tocopherol and cholesterol contents were complicated by system-by-centre interactions. There were also small differences in calcium and iron contents.
4. Riboflavin, folic acid (Lactobacillus casei) and vitamin B12 were the only nutrients which were observed to vary with the time of year in the eggs from all systems of management. Major differences were found in the vitamin content of eggs from different centres.
5. Though the differences in vitamin B12 and folic acid contents which result from the different systems of management are of little significance in an average mixed diet, they would be measurable for some individuals who may depend on eggs as an important source of these nutrients.