AbstractYoung toads were exposed to a light regimen of 12L/12D at 21°C and fed meal‐worms before hibernation in the autumn, when the toads reduce feeding and discontinue growth, and after hibernation in the spring, when feeding and growth is resumed. In the autumn treatment of the toads with bovine growth hormone maintained feeding and growth; in the spring the treatment protracted the period of feeding and growth. Thyroxin had no obvious effects on growth. It is concluded that the annual growth pattern of temperate zone toads is controlled by an internal rhythm in the secretion of growth hormo