The refractory metals are becoming increasingly important as potential structural materials for elevated temperature applications. The need for information on the strength of these materials at elevated temperatures is becoming more acute with the increase in service temperatures of the various components of power plants used in jet aircraft, missiles, rockets, and atomic reactors. Accompanying this increase in temperature are the problems associated with the satisfactory measurement of the strength of materials. Because of rapid contamination of the refractory metals and their alloys by oxygen and nitrogen at elevated temperatures, it is essential that testing be conducted in a controlled atmosphere that will reduce all possible contamination effects to a minimum . To obtain reliable and reproducible strength data, the testing chamber should be one in which a suitable vacuum, inert atmosphere, or controlled atmosphere can be maintained for extended periods of time. Possible contamination from the furnace and structural components should be eliminated. In addition, the performance of the apparatus can be improved by the elimination of ceramic materials, moving “O” ring seals, and bellows arrangements which require calibration . The time required for assembly, mounting of specimen, vacuum pumping, and stabilizing the test temperature should be as short as possible. This paper describes an elevated temperature testing machine which attempts to meet the above requirements. The chamber and heating system are designed for controlled environment as well as vacuum testing, and the mechanical details permit accurate measurement of the forces developed by the test specimen under a constant rate of crosshead motion. A constant load can also be maintained for a stress-rupture test. In this latter test the strain and strain rate are determined from the crosshead motion .