[Abnormal thyroid gland occurred in a colony of Xenopus laevis maintained at Gumma University (author's transl)].

Thyroid hypertrophy of unknown cause occurred in a colony of Xenopus laevis maintained at the Institute of Endocrinology, Gunma University, Maebashi, Japan. These animals were kept in small aquaria with well water and fed on minced pig liver. An etiologic investigation was made on the thyroid abnormality by assessing its occurrence and histopathologic features and rearing conditions of the animals in comparison with those of the colonies at Tokyo and Sendai. 1) The occurrence of abnormal thyroids was restricted within the colony of Maebashi. In the colonies at Tokyo and Sendai where animals were maintained in conditions similar to those at Maebashi, no such thyroid abnormality was noted. 2) Female animals tended to exhibit a slightly higher incidence of the thyroid hypertrophy than males. 3) Histological characteristics of the abnormal thyroid found in the colony of Xenopus closely resembled those of thyroid adenocarcinoma in man, i. e. occurrence of numerous small vesicles, multi-layered follicle cells, reduced tinctorial reaction and lowered ability to take up radioactive iodine. 4) Ever since feed replacement with pellets for trout fingerling, no individual with thyroid abnormality has been encountered in the colonies of Maebashi, suggesting that the feeding with pig liver might be a potent cause, besides water quality, for the development of abnormality described herein.