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The effect of vitamin E in maintaining the viability of tissues in animals is well known. The deficiency of the vitamin when accompanied by a selenium deficiency results in a liver necrosis in rats ( 1 ) , muscular dystrophy in rabbits (2), and exudative diathesis in chicks (3). A deficiency of vitamin E in monkeys (4) and humans under certain conditions (5) can result in a severe anemia. Explanations for the role of the vitamin in metabolism have been quite varied, ranging from its action as an antioxidant (6), protection of enzyme sulfhydryl groups (7), to a speciBfic role in the synthesis of heme (8). Our purpose in this communication is to present an approach towards the understanding of the different degrees of sensitivity of certain tissues to a vitamin E deficiency in different animals and conditions. To this end we have sought an effect of the vitamin on a variety of cells in culture, a system which is subject to specific controls by the investigator. This paper presents a method for obtaining tocopherol-free media and its usefulness in studying the utilization of the vitamin by the cell and its resultant effect on the.rate of growth.Methods. Tocopherol-free media. There are several commercially available media with no added a-tocopherol. Eagle's minimum essential medium (MEM) with Earle's salts (9) was chosen for this study. The problem, of course, comes with the uncontrolled serum component of the medium. Since tocopherol does not penetrate the placental barrier, fetal calf serum (FCS) was tested for its tocopherol content by Duggan's (10) spectrofluorometric method. No tocopherol was detected. By contrast, human serum contained 12 pg/ml and horse serum 12-24 pg/ml tocoph-erol. Addition of tocopherol to the medium was accomplished by adding 1.2 mg of d-a-tocopheryl acetate, dissolved in 0.1 ml of propylene glycol to 100 ml of FCS. The serum was then filtered through a 0.45 pm Millipore filter. The filtration resulted in about a 20% loss of the vitamin. The serum was added to MEM at a level of 10%. Thus, the !final concentration of d-a-tocopheryl acetate was about 1 .O pg/ml medium.Uptake of d-a-t ocophsryZ-3,4-I4 C-acet at e. The cells used in these experiments were (fibroblasts obtained from seminiferous tubules of a Chinese hamster, isolated by Dr. C . Yerganian, and are now a secondary derivative of a primary diploid strain. They are designated STBTL cells. The cells were grown to about three quarter confluency in 5 cm plastic dishes (NUNC, Vanguard International) in MEM (Earle's) with 10% FCS. The medium was removed and replaced with MEM containing 2.5% FCS with 13.7 pg/dish d-utocopheryl-3 ,4-14C-ace tate obtained through the generosity of W. E. Scott of Hoffman La Roche. At a given time interval two duplicate dishes were taken, the medium removed, the cells washed thrice with phosphate buffered saline and drained. One milliliter of deionized water was added to each dish and allowed to stand for 30 min to cause cell lysis. The plates were scraped with a rubber policeman and the cells uniformly susp...