1. The temperature near the carotid artery has been measured in the unrestrained pig by means of radiotelemetry. When the animals were housed singly under constant conditions of temperature and lighting the temperature rhythm appeared to be related only to the time of feeding. A similar record was obtained from temperature measurements made in the hypothalamus.2. Over the range of ambient temperatures 10–30° C the mean body temperature was 38·8° C. No consistent variation occurred with ambient temperature, but on initial transfer from 10 to 30° C ambient temperature the body temperature decreased, while on initial transfer from 30 to 10° C it increased.3. When one pig was housed in a hut with a small outside yard a nychthemeral rhythm was sometimes superimposed on that imposed by feeding. When two pigs were kept in a paddock containing a hut the nychthemeral rhythm was more pronounced.4. It is concluded that in the pig there is very little innate circadian temperature rhythm and that the temperature variations seen are related chiefly to feeding and activity.