Studied were the morphologic changes in the viscera of 14 sheep and 2 goats experimentally intoxicated via the oral administration of simasin at various rates. The gross lesions consisted of catarrhal and hemorrhagic typhlitis, liver dystrophia, and enlargement of the gallbladder. Histologically, the acute cases presented granular degeneration of the liver and kidneys, oedema of the lungs, fatty infiltration of the myocardium, oedema, hyperemia, and hemorrhages in the brain. In the cases of chronic intoxication there were fatty degeneration of the liver as well as dystrophic changes in the testes, cerebrum, and cerebellum and diffuse granular degeneration of the kidney. Chronic intoxication of sheep with simasin at 1.4 and 3.0 mg per kilogram led to hypofunction of the thyroid; doses of 6.0 and 25 mg kg caused colloid struma while acute toxicity with 250 mg/kg (once and twice treated animals) caused parenchymal struma. A drop in the content of liver glycogen and degranulation of the mastocytes of the mesentery were also observed.