The effects of bilateral lesions in the lateral hypothalamus (LH) of the rat on several thermoregulatory and non-thermoregulatory variables were studied. In agreement with the literature, a reduction in food and water intake and in body mass were observed in the experimental animals but not in the operated controls. Rectal temperature and metabolism increased for a few hours after the lesion, decreased below pre-lesion level for a day or two, and finally returned to baseline level. The increase in rectal temperature during a 1-hr exposure to 5 degrees C was accentuated in the control but not in the experimental subjects. An improvement in operant thermoregulatory behavior, measured by nose-poke and lever-press responses, was observed in most LH-lesioned animals. Thermal preference in a gradient, two measures of general activity, and light avoidance were not affected by the lesions. The post-lesion improvement in operant thermoregulatory behavior does not support the view of the LH as a necessary locus for the integration of behavioral thermoregulatory responses.