In the Cornell C strain of White Leghorn chickens, thyroiditis appeared spontaneously. It was characterized by phenotypic changes due to a decrease of thyroxine, histological damage to the thyroid gland, and the presence in the seruim of antibodies to thyroglobulin. Susceptibility to the disease is genetically inherited. Hormonal bursectomy (androgen given to the embryo) suppresses the development of thyroiditis.