To test whether vitamin E deficiency might influence the course of essential fatty acid (EFA) deficiency, Long Evans rats were fed diets containing a marginal amount (1.5% of calories) of 18:2 omega 6 or 18:3 omega 3 fatty acid with complete absence of the other and with or without vitamin E. Vitamin E contents decreased continuously in serum and liver in all rats fed the E-free diets but in the brains of only the rats fed the marginal 18:3 omega 3, E-free diet. It is considered that the vitamin E is cooxidized in the liver with 22:6 omega 3, since this fatty acid is very low in livers of the rats fed the marginal 18:2 omega 6 diet but much higher in livers of the rats fed the marginal 18:3 omega 3 diet. Brain 22:6 omega 3 values are comparable for both groups. The source of 22:6 omega 3 is evidently in the mother's milk, since following weaning there is a precipitous drop in 22:6 omega 3 in serum, liver and carcass of rats on the 18:2 omega 6--containing diet. No significant signs of EFA deficiency were seen in the E-deficient rats.