The Rayleigh wave velocity on an otherwise isotropic‐free surface is changed by the application of a static stress. A technique is described for calculating these changes as a function of the third‐order elastic constants and the static stress configuration. Conversely, these velocity changes can be used to measure the third‐order elastic constants. These corrections in the velocity appear as additional terms to the isotropic Rayleigh equation. Three independent Rayleigh velocity measurements are sufficient to determine the third‐order elastic tensor for an isotropic solid. Experimental data is provided to validate the calculated results.Subject Classification: [43]35.26; [43]20.35; [43]35.54.