In order to obtain a correlation of adrenal cortex with biochemical function, ultrastructure was closely studied statistically and morphometrically. For the purpose of evoking fluctuations in the function of the adrenal cortex, whole body X‐irradiation (1,000 R), ligation and reopening of the adrenal artery and vein, Metopiron administration, hypophysectomy and ACTH administration were carried out. Whole body X‐irradiation caused hyperfunction of the adrenal. Ligation of adrenal artery and vein caused adrenal hypofunction with a tendency to recovery after release. Metopiron administration and hypophysectomy caused hypofunction of the adrenal cortex. In the mitochondria, ferricyanide reduction by dehydrogenase systems was found in the inner vesicles. The results of morphometrical studies on the correlation of biosynthetic function of the cortlcoids and morphological changes revealed an increase in volume of the crlstae, an increase in number and enlargement of mitochondria, and an increase and dilatation of smooth‐surfaced endoplasmic reticulum at the time of hyperfunction of the adrenal cortex. At the time of hypofunction of the adrenal cortex, the volume increase of mitochondria accompanied by shrinkage of the crlstae were noted. The smooth‐surfaced endoplasmic reticulum showed a tendency to narrowing and d