A polystyrene latex suspended in HCl has been studied by dielectric response and dynamic mobility measurements. The aim was to see if these data, along with previous results from other techniques, could be interpreted in a consistent way within the standard electrokinetic model to yield information about the surface electrical properties of the latex. It was found that the zeta-potentials deduced from dynamic mobility and conductivity measurements were reasonably consistent, but did not agree well with those deduced from the electrophoretic mobility. The use of a dynamic Stern layer did not improve the agreement to any great extent. It is conjectured that differences in the methods of preparation, in particular the use of centrifugation, may be responsible for some of the disagreement. The pH-dependence of the dynamic mobility was also investigated and found to be weak. The dielectric response measurements showed significant discrepancies from the predictions of the standard electrokinetic model in the kHz regime, and the dynamic Stern layer model with realistic parameters could not improve the agreement very much. However the experimental relaxation frequencies were in good agreement with the predictions of the theory. Copyright 1999 Academic Press.