Urine flow and compositions were determined in normally hydrated, waterloaded and hypotonic saline infused hens under various ambient temperatures (Ta). 2. At Ta 29 and 32 degrees C normal urine flow was reduced and osmolality increased; at Ta 0 and -5 degrees C urine flow increased and osmolality decreased. 3. In hydrated hens at Ta 32 degrees C antidiuresis occurred within 10 min and persisted for 2 hr without any significant change in rectal temperature (Tr). 4. At Ta 40 degrees C there was no antidiuresis but a tendency for urine flow to increase; Tr also rose. The antidiuresis shown by water-restricted hens at Ta 20 degrees C was abolished at Ta 40 degrees C. 5. An antidiuresis, similar to that seen at Ta 32 degrees C, could be produced at Ta 20 degrees C by moderate haemorrhage, exposure to infra-red heating or by vasopressin or vasotocin. Adrenaline and noradrenaline provoked a diuresis. 6. Hypothalamic heating failed to elicit an antidiuresis but hypothalamic cooling increased urine flow at Ta 20 degrees C and abolished the antidiuretic response at Ta 32 degrees C. 7. It is concluded that the antidiuresis seen at warm ambient temperatures is caused by the release of antidiuretic hormone possibly as a response to a rise in skin temperature.
