Histologic observation was made on the lesons in various endocrine glands of the mouse and rabbit caused by hydrogen sulfide poisoning. The results are briefly summarized as follows: 1. The Hypophysis. In the anterior lobe, the chromophobe cells markedly decreased in number and displayed an irregular arrangement. The alpha cells showed the decrease of acidophilic granules in number and of cytoplasm in size, and the younger forms of the alpha cells markedly increased. The beta cells increased both in size and in number with the cytoplasm crowded with basophilic granules. The cells in the pars intermedia were deeply stained, the cytoplasm becoming compact in structure. 2. The Pineal gland. The gland cells showed a considerable atrophy, the cell borders becoming less distinct, and pycnotic nuclei seeming to crowd closely together. 3. The Thyroid gland. The lumens of the follicules were dilated with a marked increase of diluted colloid in amount. The colloid became quite homogenous with the disappearance of all vacuoles, and the follicular epithelium showed a low cuboidal or flat form. 4. The Parathyroid glands. The principal cells increased in size with the cytoplasm crowded with deeply stained granules in their central zone and faintly stained in their peripheral zone. The nuclei were also large in size, having vesicular appearance. 5. The Thymus. The bulk of the thymus was increased in general. The cortical cells decreased in number, the cortex thinning remarkably, while the medulla showed generally a marked hyperplasia, especially the Hassal's bodies increased in number showing a marked hypertrophia with advanced hyperkeratosis. 6. The Adrenal glands. The cells of the zona glomerulosa in the cortex showed hyperplasia with an abundant cytoplasm and vesicular nucleus. The lipid content in the cells of the zona fasciculata was decreased, and their cytoplasms were stained deeply. The bulk of the medulla was increased by the hypertrophy of the medullar cells with polygonal cytoplasm crowded with deeply stained granules and a large vesicular nucleus embedded. The chrome reaction proved highly positive. 7. The Testis. Decline or absence of spermatogenesis was seen in some parts of the seminiferous tubuli. In some cases, the seminiferous epithelium occasionally displayed a marked atrophy or degeneration. The changes mentioned above showed no difference in quality but in intensity according to the kind of animals and methods used.