Dogs with impaired heat regulation had a definitely raised thermal threshold; they were able to discriminate the sensation of warmth only at high levels of stimulus intensity. The 75% correct choice threshold for the normal dog varied from about 1.6 to 13.6 millicalories per square centimeter per second (mc/cm2/sec.). The 75% correct choice threshold for the dogs with hypothalamic ablations trained under identical discrimination conditions varied from 46.2 to 72.6 mc/cm2/sec. Since the learning ability of the operated dogs was also found to be impaired, it is not possible to state whether the raised threshold was due to sensory impairment, learning impairment, or a combination of both. Serial sections of the operated brains revealed that damage was localized to the hypothalamus in one animal. Therefore, it is suggested that damage to the hypothalamus per se accounts for the ‘functional’ high thermal threshold rather than involvement of other neurological structures.