Abstract: A duplex thermocouple assembly for operation in a high pressure environment and to have a rapid response time. The assembly consists of two small diameter thermocouples and a fitting designed to protectively hold the thermocouples. The thermocouples are soldered into two axial channels which extend along the length of a stainless steel cylinder which forms a portion of the protective fitting. At the temperature sensing end of the assembly the ends of the thermocouples project slightly beyond one end of the cylinder. The cylinder is soldered at its other end into a hole axially drilled in one end of a larger stainless steel cylinder so that both cylinders form a protective fitting for the thermocouples.