Lymphocytic infiltrates in the thyroid gland are found in a variety of diseases: Hashimoto's disease, lymphocytic thyroiditis, thyrotoxicosis, nodular goiters, and in relation to neoplasms of the gland. The degree of replacement of thyroid parenchyma by the lymphocytes varies from the diffuse infiltrates in thyroiditis to focal and often small accumulations of lymphocytes in nodular goiters and in carcinomas. A recent survey1 of surgical thyroid diseases at the University of Michigan Medical Center, Ann Arbor, demonstrated a significant change in the morphological appearance of thyroid glands following the introduction of iodine for therapy (1922) and prophylaxis (1924). The salient histopathological feature of the thyroid glands, removed at operation in a five-year period before iodine prophylaxis (1915 to 1920), was the paucity of lymphocytes in their parenchyma, and, more importantly, the absence of thyroiditis of any form. After the introduction of the therapeutic and prophylactic use of iodine, a steadily