The surface-charge characteristics of viruses in water can strongly influence their behavior with respect to physicochemical processes like coagulation and filtration. In the past, characterization of this surface charge by whole-particle microelectrophoresis has been limited to relatively large viruses, primarily due to difficulties in visualizing the individual virus particles. Here, we demonstrate a new approach for performing microelectrophoresis measurements which permits the surface characterization of even very small viruses. Our approach differs from conventional microelectrophoresis measurements in that virus particles are visualized by light scattering, employing a green laser (wavelength = 544 nm) as the light source. We demonstrate this technique by characterizing the electrophoretic mobilities and isoelectric points of two viruses-bacteriophage MS-2 and lambda (lambda strain cI47)-which differ in their shape and size.