SUMMARY: The endocrine glands of the protein-calorie deficient animals were smaller than those of pigs of the same age normally fed. However, relative to body weight, the adrenals were large, the hypophysis within the normal range, the thymus small and the pancreas and thyroid showed wide variations attributable to different degrees of oedema. In the tissues of the endocrine glands of the protein-calorie deficient animals the cells exhibited a loss of cytoplasm and, when normally present, of secretory granules, the severity of the change varying widely between the different organs of the same animal. Thus the exocrine portion of the pancreas was more severely affected than the islet tissue; within the latter β cells showed greater changes than did α cells. The cells of the thyroid gland were flattened and epithelioid in shape and those of the hypophysis were small, with many partially or wholly degranulated chromophiles. The zona fasciculata of the adrenal cortex was usually less severely affected, with, at some stages, a relatively excessive activity which contributed to the precarious endocrine balance. Since most of the animals were killed before sexual maturity less attention was given to the gonads. Testes, however, appeared to be affected by the deficiency to a greater extent than did ovaries. The relationships between protein-calorie deficiency, hypophysectomy and an excess of corticosteroids are discussed. It is suggested that in protein-calorie deficiency, an adequate supply of protein for anabolic purposes is the primary factor with a subsequent alteration in hormonal secretions playing an important, but secondary, role.