CHRONIC treatment, with a constant dose per animal or per kg., of either purified bovine anterior pituitary growth hormone, or crude growth hormone containing extracts of bovine or rat pituitaries, fails to produce continuous growth, indefinitely, in either intact or hypophysectomized Norway rats (1, 2, 3, 4, 5). Treatment with growth hormone at a high dose level will give continuous growth for as long as a year and produce rats as large as 2.5 times normal adult size, yet plateauing still occurs (6, 7). That this phenomenon of plateauing on a constant dose of growth hormone is not merely a reflection of age changes in the animals is shown by the fact that senile rats, older than any used in any of the above mentioned experiments, show as great a growth response to growth hormone as do young adults (5). It has been shown by Selye that plateauing occurs at a higher weight level if DCA is given along with growth hormone in the intact rat (2), and that the initial growth response to growth hormone in the adrenalectomized rat requires either a mineralocorticoid, or NaCl in excess of that present in Purina Fox Chow (8).