The measurement of electrophoretic mobility is commonly done by laser Doppler electrophoresis (LDE). Recently, a more sensitive technique, phase analysis light scattering (PALS), has been developed with particular benefits for application to nonpolar systems. We have carried out PALS measurements of the electrophoretic mobility (mu) of modified silica particles as a function of applied electric field. Our results are in poor agreement with LDE measurements on the same system. We show that this difference might result from the way in which PALS measurements are performed and suggest that, in this case, the known field-dependent mobility will cause artifacts in the PALS data. When the mobility is field-dependent, this factor must be accounted for appropriately in PALS data analysis.