The direction of this project is much as before: 1) to elucidate the pathogenesis of Graves' disease by studying the immune mechanism involved; 2) to continue a 5 years experience in the therapy of Graves' disease with I 125 to determine if the late, high incidence of hypothyroidism which follows I 131 treatment can be avoided; 3) to establish better methods of diagnosis of thyroid disorders or to simplify existing methods; 4) to study further thyroid function in the spontaneously hypertensive rat.