The effect of hypothalamic lesions on temperature regulation was studied in pigeons by recording deep and skin temperatures, shivering, panting and oxygen consumption. Thresholds of shivering and panting were assessed before and after lesions. Survival was 100% when lesions were done in awake animals in a cool environment. Lesions anterior to the anterior commissure which included the preoptic area resulted in an increased threshold of panting or a lack of panting response at body temperatures up to 44.5 degrees C. Shivering response was unchanged in these animals. Lesions posterior to the anterior commissure were followed by a lack of shivering response with no change in panting threshold. This points to a segregation of the hypothalamic structures controlling heat loss and heat gain in the pigeon.