A responsive microthermocouple probe with a time constant of 2-3 ms was constructed using a fabrication method for glass microelectrodes as widely utilized in neurobiology. The probe is composed of a constantan wire of 25 μm in diameter and a vapor-deposited copper film of 1.8 μm in thickness. These two components come into contact at the tip of a glass pipette, forming a sensing junction of approximately 17 μm in diameter. The thermoelectromotive force of 40.2 μV/°C is very close to the standard value of the International Electrotechnical Commission and linearly dependent on temperature over the range normally encountered in biological measurement. The microthermocouple probe was tested by insertion into a dorsal longitudinal muscle of a silkworm moth. The core temperature was found to rise rapidly by 10-11 °C after pheromonal stimulation, returning to the original temperature at rest in 15-20 min. Moreover, the probe was used successfully to measure the temperature variation in the thorax of a cockroach without damage to the tissue.