By measuring the distribution in electrophoretic mobility of dispersed colloidal particles as well as their size distribution, detailed information can be obtained about the electrokinetic properties of the surfaces of the particles. Instead of characterizing a colloidal particle solely by its ζ-potential, knowledge of the mobility and size distribution allows the determination of other parameters, such as the Stern potential, the thickness of the immobilized surface layer, and the anomolous surface conductivity in this immobilized layer or in the Stern layer. Model calculations are presented to show how this information can be obtained.