Since young animals put on an A-free regime at weaning begin to fail from lack of A as early as the 50th day of life and on an E-free diet regularly retain a normal seminiferous epithelium and fertility until the 90th day of life, the period between the 50th and 90th day, when stores of vitamin E are still intact, would seem to be the period best adapted to proving the effect of vitamin A deficiency. Experiments on 24 young [male] rats, 8 fed a diet low in A at weaning, 8 fed the same diet plus 6 drops wheat germ oil daily (high E, low A) and 8 fed the same diet plus 2 drops of cod liver oil daily (high A, no supplementary E) showed that in young [male][male] the stores of vitamin A are more rapidly depleted than those of vitamin E, and that with depletion of A there is marked deterioration of the seminiferous epithelium. Of 20 rats fed on A-free diet supplemented by 6 drops of wheat germ oil, 10 received also 2 drops of cod liver oil daily. The group reared on the low A diet (without cod liver oil) became sterile and showed marked degeneration of the testes by the 3d mo. of life. The fertility of the group reared on adequate A diet (with cod liver oil) was unimpaired and the organs were normal at autopsy.