It has been shown1that infant rats which were stimulated daily from birth exhibited significant depletion of adrenal ascorbic acid when subjected to cold stress at as early as 12 days of age, whereas nonstimulated, control infants did not show significant depletion of adrenal ascorbic acid to cold stress until 16 days of age. These results were interpreted as indicating that one of the effects of infantile stimulation was to accelerate the maturation of the hypothalamohypophysial system, inasmuch as depletion of adrenal ascorbic acid to cold stress appears to depend upon a functional hypothalamohypophysial system. Since in the previous experiments we investigated the maturation of a functional system, we were interested in determining whether structural components of brain tissue also showed differential maturation as a function of infantile stimulation. Accordingly, the present report presents the results of experiments comparing the amount of cholesterol present in