1. The adrenal cortices of rats injected chronically with pituitary growth hormone showed an increase in nodularity as compared with the controls. There was no other evidence of stimulation of the adrenal cortices of the experimental rats.

  2. The adrenal medullary tissue was increased in amount in all rats injected chronically with growth hormone. The increase was due to cellular hypertrophy and proliferation.

  3. In ten of fifteen rats injected chronically with pituitary growth hormone, there were areas of neoplastic cells displacing and invading the adrenal cortex. In three of the rats, the neoplastic medullary tissue had grown through the cortex and was macroscopically visible on the surface of the adrenal gland.

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Aided by grants from the U.S. Public Health Service RG-409; the Research Board of the University of California; the American Cancer Society, Inc., N.Y.; and the University of California Cancer Grant.

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