alpha-Tocopherol has near optimal activity as a chain-breaking antioxidant. Inherent antioxidant activity plays an important part in determining overall biological activity but the phytyl tail also exerts a very important influence. The new deuterated alpha-tocopherol/GC-MS technique is providing unprecedented insight into the importance of the stereochemistry of the phytyl tail in determining bioavailability, as well as helping to discover how rapidly and effectively absorption, transport, uptake, and loss occur. Measurements of rate of turnover in tissues indicate that differences exist between different types of animals. It is possible that these tissue differences may explain the diverse range of vitamin E deficiency symptoms observed across a wide variety of animals. It is not known what is responsible for the differences in biokinetic behavior.