Recent work on ion−implanted metals has demonstrated the existence of substantial changes in friction and wear properties brought about by ion implantation. The effects have been attributed to corrosion inhibition, metallurgical transformation, or mechanical surface hardening. In the work to be presented, a capacitance probe apparatus is described which has been used to detect the deflection occurring during ion implantation of thin specimens of annealed steel. The deflection is related to the introduction of a surface compressive stress. 100−keV argon ion implantation is found to produce surface stresses of several thousand lbs/in.2 which reach a maximum at a dose approximately 5.0×1016 ions−cm−2. Light ions, such as nitrogen, which form chemically stable compounds within the steel, generate similar stresses within the surface such that a macroscopic deflection of the specimen can be observed. In this case very high doses are required to maximize the stress (∠1017 ions−cm−2). The results are interpreted with reference to damage mechanisms and nitride formation, and are discussed in relation to the mechanical property changes previously reported.