Abstract: An infrared temperature probe for high pressure use is in the form of a hollow bolt adapted to be threaded into a complementary threaded aperture in the wall of a pressure vessel with the end thereof disposed flush with the internal surface of the pressure vessel wall. An infrared transparent window is secured in the end of the hollow bolt with one surface thereof disposed flush with the end of the bolt. A bundle of optical fibers is secured within the opposite end of the hollow bolt and a glass rod is mounted within the hollow bolt in operative relation to the window and the optical fiber bundle for transmitting infrared radiation from the window to the optical fiber bundle. The interior of the hollow bolt may be supplied with a circulating cooling liquid or gas.