The microscopic changes in this type of goiter in humans, first described in 1925 by the same authors, are traced from the early stages of lymphocytic activity to the terminal stages of fibro-sis and atrophy. Many goiters belonging to this group have been called by earlier observers "chronic inflammatory thy roiditis," "endothelioma," "sarcoma," "Rie-del''s disease," or "woody thyroid." A previous postulate that such a thyroid is associated with some general constitutional disorder ending in myxedema was revived in a search for the etiology. McCarrison reproduced the earlier stages of the goiter in rats by giving a diet composed largely of white flour or other vitamin-poor carbohydrate, vitamin-poor protein, and vitamin-poor fats and in which there is a paucity of fresh fruit and green leafy vegetables. It is thought that the terminal stage of lymphadenoid goiter can also be produced in rats, if they can be kept alive long enough. The widespread use of white flour and other vitamin-poor foods in western countries, together with the small proportion of fresh fruit and green leafy vegetables, renders the etiological significance of the observations on rats very great.