In 40 experiments on seven goats head and trunk temperatures were altered independently of each other and the effects on exercise performance on a treadmill (speed: 3 km/h, slope: 16%-20%) were observed. Brain temperature between 38.5 degrees C and 42.0 degrees C and trunk temperature between 39 degrees C and 43.5 degrees C did not reduce exercise performance or running time. Blood lactate concentration increased with rising brain and trunk temperatures, but did not exceed 13.1 mmol/l-1. Blood pressure and heart rate did not show any dependence on brain or trunk temperatures. Brain temperature between 42.0 degrees C and 42.9 degrees C shortened running time in 3 out of 12 experiments and reduced performance during shortlasting upward deviations of temperature. This suggests that in this species, the thermal safety limit to exercise is very close to that range of temperature which is likely to induce heat stroke.