It is widely held that selective brain cooling, the lowering of brain temperature belowarterial blood temperature, and adaptive heterothermy, the use of heat storage to reduce body water lossby evaporation, are crucial for the survival of large mammals in arid-zone habitats. These ideas arose 35years ago as a consequence of work popularised on the eland and the oryx. However, brain temperaturein these antelope was never measured. Also, the evidence that these large antelope use adaptiveheterothermy was derived from experiments using captive animals. The development of miniaturedevices for remote sensing of body temperature now has allowed temperatures of free-living animals intheir natural habitats to be recorded.With the exception of dehydrated Arabian oryx exposed to severeheat, free-living eland and oryx do not exhibit adaptive heterothermy, and have a mean bodytemperature at night higher than that during the day. Eland and oryx exhibit selective brain cooling ofsmall magnitude (b0.5 8C) sporadically, at rest under moderate heat load. The view that eland and oryxroutinely use adaptive heterothermy to save water and selective brain cooling to protect the brain ismisleading, and arises from inadequate measurement or from depriving animals of access tothermoregulatory behaviour. D 2004 Elsevier B.V. All rights reserved.