The anther has examined the variations of juxtaglomerular index (J. G. I. ) of kidneys and zona glomerulosa of adrenals in rats with various conditions affecting the renin and aldosterone production. (1) It has become evident that the J. G. I. and zona glomerulosa index (Z. G. I.) in rats fed on a low sodium food were apparently increased and the production of both renin and aldosterone were deeply related with electrolytes especially sodium concentration in plasma. (2) The J. G. I. and Z. G. I. in rats administered with DOCA or aldosterone showed the same tendency, while the ones administered with hydrocortisone did not show such remarkable changes. (3) In a short period administration of synthetic angiotensin II J. G. I. showed a decreasing tendency. From this fact a small dosis of angiotensin II seemed to work to cause directly the inhibition of renin secretion. On the other hand Z. G. I. was increased up to after one week of angiotensin II administration because angiotensin II works as an aldosterone stimulating factor. Thereafter (after two weeks) both J. G. I. anc Z. G. I. showed a tendency of decrease probabely due to a suppressing effect of increased aldosterone to renin secretion. (4) In Goldblatt hypertensive rats J. G. I, increased in kidney with renal artery constriciton and decreased definately in the contralateral kidneys.