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A ratio of 1.36:1 in relative bioactivity of RRR-α-tocopheryl acetate as a natural (Nat-α-T) source to all-rac-α-tocopheryl-acetate, as a synthetic (Syn-α-T) source, is generally accepted. This factor also largely reflects the difference in bioavailability. However, studies indicate that neither bioavailability of α-tocopherol stereoisomers nor relative bioavailability between them are constant, but are dose-dependent and differ between organs. However, no information is available about how different ratios between synthetic and natural α-tocopherol affect bioavailability of α-tocopherol stereoisomers. Thirty lambs were randomly assigned to diets supplied with additives containing 5 different Syn-α-T to Nat-α-T ratios, including 100:0, 75:25, 50:50, 25:75, and 0:100. The experiment lasted for 70 d after which the lambs were slaughtered. The amount of RRR-α-tocopherol generally increased in plasma and organs with increasing the proportion of Nat-α-T in the diet (P < 0.05). However, the relative bioavailability of RRR- and RRS-α-tocopherol in plasma, organs, and abdominal fat generally decreased with increasing the proportion of Nat-α-T in the diet (P < 0.05), whereas the other stereoisomers only showed minor changes with the exception of liver. However, a linear response was maintained between the ratio of stereoisomers in the feed and the ratio in plasma and organs. In conclusion, regardless of Syn-α-T to Nat-α-T ratio in the diets, amounts of α-tocopherol stereoisomers in plasma, brain, heart, lungs, and abdominal fat were in the following order: RRR > RRS, RSR, RSS > Σ2S., (© The Author(s) 2019. Published by Oxford University Press on behalf of the American Society of Animal Science. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)