A low‐pressure pneumatically controlled stressing mechanism for investigating the effects of uniaxial stress on the magnetostrictive and magnetomechanical behavior of 2% Mn pipeline steel is described. The apparatus uses microcomputer control and data logging. It has been developed to allow convenient stress cycling so that reversible and irreversible changes can be separated. Irreversible stress‐induced changes in magnetization are toward the anhysteretic, in accordance with Jiles–Atherton theory. Reversible magnetomechanical effects may be correlated with reversible magnetostrictive effects.