A single external gamma-irradiation (1 Gy) of rats on day 35 of their life causes stable structural and functional disturbances in the thyroid gland leading to the development of hypothyrosis at the remote times following irradiation which is demonstrated by the decrease in the concentration of thyroxine in the blood, increase in the thyrotropic function of the hypophysis and inhibition of the activity of tyrosine-dependent enzyme, alpha-glycerophosphate dehydrogenase, in the liver. Disturbances induced by such exposure in the thyroid gland of adult rats are insignificant and compensatory in time.