Abstract: A probe for measuring temperatures in a hot gaseous medium such as the gases inside the shaft of a blast furnace. A first tubular member extends from a base structure such as a blast furnace wall into the gaseous medium. Successively smaller, second and third tubular members are concentrically positioned inside this exterior tubular member. Preferably, an exterior protective member also surrounds the first tubular member. A refractory material is interposed between the exterior protective member and the first tubular member to minimize temperature fluctuations in the body of the probe itself. Thermocouple leads extend longitudinally in an air space between the second and third tubular members and then protrude to the exterior of the probe. A forward fluid coolant passageway is formed inside the third tubular member.