Phase-selective fundamental and second-harmonic tensammetry show that the desorption of uncharged surfactants is strongly influenced by the supporting electrolyte in the region of the desorption peaks. Quantitative data, however, can be extracted only if assumptions are made about adsorption isotherms, and in particular about the potential-dependence of the surface coverage around the desorption peaks. A satisfactory model and theoretical treatment has to be developed. In the meantime, such studies can provide useful empirical data.