Using high-speed steels T–1 cold M–50, which have little amount of retained austenite and the usual through-hardening ball bearing steel SUJ 2 (SAE 52100) previously tested, changes in x-ray parameters with loading cycles in rolling contact were examined and the following formula between loading cycles and x-ray parameters was found: N = K·(δB)6·(δσ)3·(δγ)0, where F = (δB)6·(δσ)3was defined as “fatigue parameter” and δB δσ, δγ are changes in half-height breadth, residual stress, and retained austenite, respectively. If we know in advance the value of Fc, the fatigue parameter at which a surface-originated fatigue failure results, the ratio of F at a given number of loading cycles to Fc gives the life ratio N/Nc, which is the ratio of loading cycles N to the loading cycles Nc when a surface originated fatigue failure would occur. Fc was about 1 for various materials and test conditions, if we use units of residual stress value in GPa and half-height breadth in degree of diffraction angle.Presented at the 42nd Annual Meeting in Anaheim, California May 11—14, 1987