  We propose a model for the nonequilibrium enhancement of colloidal
self-diffusion in an externally imposed shear flow in charged systems. The
enhancement of diffusion is calculated in terms of the electrostatic, two--body
interactions between the particles in the shear flow. In the high shear rate,
low volume fraction limit in which our model is valid, we compare these
calculations to the experiments of Qiu et al. [Phys. Rev. Lett. 61, 2554
(1988)].
