Abstract: A hollow dipstick is provided for immersion in molten material to determine the temperature of the molten material at any desired depth. The hollow dipstick is connected to an infrared detector by means of an optical fiber bundle for producing a signal indicative of the temperature of the molten material. An infrared focusing lens is provided within the hollow dipstick for transmitting the infrared radiation from the interior bottom surface of the dipstick to the fiber optic bundle. A container having a heating element therein is provided for receiving the dipstick when it is not in use so as to preheat the dipstick to a temperature close to the estimated temperature of the molten material to be measured to thereby prevent thermal shock to the dipstick upon immersion in the molten material. Alternatively the infrared detector is mounted directly on the dipstick.