Exptl. goiter was produced in chicks by feeding a ration containing 0.145 mg. of iodine per kg. and prevented by the addition of 5 mg. of I per kg. to the same ration. Thyroid weights of chicks fed the basal diet were 130, 240, and 294% of those of the control group at 6, 12, and 18 weeks of age, respectively. The histopathological conditions of the enlarged thyroids are described.