This paper deals with the activity of pyrogenal (50 μg/kg) upon the functional state of the thyroid gland. Determining the level of the tiroxin (T4) and 3-iodtironin (T3) at white rats that were administered pyrogenal, we ascertain a rapid growth of these hormones. Essential changes were of 50 established in the thyroid gland structure. the administered MSH on the pyrogenal background has a protective role for thyroid gland normalizing the modifications that had taken place.