AbstractThe changes in the levels of blood sugar and plasma cholesterol and the histology of the pancreatic islets were studied following hypophysectomy in the snake,Natrix piscator.Hypophysectomy inN. piscatorproduced a progressive decrease in glycemia and after 15 days, an aglycemic condition developed accompanied by slight degranulatory changes in the alpha cells of the pancreatic islet tissue. A significant decrease in the muscle glycogen concentration was also noticed 15 days after the operation. Atrophic changes were evident in the thyroid and adrenal glands of the operated animals.An extract of three pituitaries when injected in a normal snake did not produce any change in the blood sugar level. It is suggested that the absence of a diabetogenic action following injection of pituitary extract may be due to the opposing action of the endogenously produced insulin in the intact pancreas of the animal.