We have used thermistor/data logger assemblies to measure temperatures in the brain, carotid artery, jugular vein and abdominal cavity, and subcutaneously, in five pronghorn antelope over a summer in Wyoming. Globe and air temperature varied by up to similar to 50 degrees C daily during the summer and maximum solar radiation was similar to 900 W m(-2). Brain temperature (38.9 +/- 0.3 degrees C) was consistently similar to 0.2 - 0.5 degrees C higher than carotid blood temperature (38.6 +/- 0.3 degrees C), which was the same as abdominal temperature (38.8 +/- 0.4 degrees C). Jugular blood temperature (38.0 +/- 0.4 degrees C) varied, probably because of changes in Respiratory Evaporative Heat Loss (REHL), and was lower than other temperatures. Subcutaneous temperature (38.3 +/- 0.6 degrees C) varied, probably because of peripheral vasoactivity, but on average was similar to other temperatures. Carotid blood temperature had a circadian/nycthemeral rhythm weakly but significantly (r = 0.634) linked to the time of sunrise, of amplitude 0.8 +/- 0.1 degrees C. There were daily variations of up to 2.3 degrees C in carotid body temperature in individual animals. An average range of carotid blood temperature of 3.1 +/- 0.4 degrees C over the study period was recorded for the group, which was significantly wider than the average variation in brain temperature (2.3 +/- 0.6 degrees C). Minimum carotid temperature (36.4 +/- 0.8 degrees C) was significantly lower than minimum brain temperature (37.7 +/- 0.5 degrees C), but maximum brain and carotid temperatures were similar. Brain temperature was kept relatively constant by a combination of warming at low carotid temperatures and cooling at high carotid temperatures and so varied less than carotid temperature. This regulation of brain temperature may be the origin of the amplitude of the average variation in carotid temperature found, and may confer a survival advantage.