An easily constructed apparatus is described for applying tension and compression stresses to metal and alloy samples while being subjected to x‐ray diffraction analysis. The back reflection technique is employed in which diffraction patterns can be photographed in five minutes or less. The apparatus and technique have been developed because of the increasing interest in the measurement of strain in a variety of metallurgical materials of primary war interest. A series of patterns on a familiar aluminum alloy under calibrated tension stresses is reproduced as an example by means of which evaluation of residual strains in large castings can be non‐destructively evaluated.