The electrokinetic potentials at high ionic strengths can be measured by means of electroacoustic method. The reported values are surprisingly high: up to 25 mV in 1 mol dm(-3) 1:1 electrolyte solution. The IEP of metal oxides in concentrated solutions of 1:1 electrolytes shifts to substantially higher pH values with respect to the pristine value, although these electrolytes are inert at low concentration. The shift in the IEP is salt-specific, and it is correlated with the hard-soft character of the anion and of the cation.