The retrospective mini-review contains contemporary literature data about biological importance of change in the blood level of calcitonin under different conditions of carbohydrate metabolism. An increase in calcitonin activity value and a decrease in plasma concentration of total calcium in rats of all age groups were established in hypo-and hyperglycemia. More noticeable hypocalcemia and hyper calcitoninemia in glucose tolerant test and more intensive changes in calcitonin secretion and hypocalcemia in insulin hypoglycemia were detected in immature rats than in adult and old rats. A conclusion was made that biological significance of a rise of calcitonin in different conditions of carbohydrate metabolism was body calcium saving.