An apparatus is described that can determine electrophoretic mobilities of polar and non-polar colloidal dispersions down to -12 2 10 msV -1 -1 with typical resolutions of 0.5 to 5%, depending on the nature of the dispersion being studied. The diffusion coefficient and settling/convection velocity of the sample may be determined simultaneously in real time with the electrophoretic mobility. The technique, phase analysis light scattering (PALSY, is based upon classical laser-Doppler electrophoresis, but employs signal processing of the time domain phase information within the scattered light signal, rather than analysis of its frequency spectrum. This allows much smaller electric field strengths to be employed, thereby alleviating the usual heating problems associated with electrophoretic studies of non-polar dispersions. PALS measurements of typical aqueous latex dispersions with large mobilities and non-polar dispersions with very small mobilities (down to 5x 10_12 m2 s-1 V-1) are presented to illustrate the versatility of the technique.