  Coupled spin-charge drift-diffusion equations are derived for a biased
two-dimensional electron gas with weak Rashba spin-orbit interaction. The basic
equations formally agree with recent results obtained for spin-orbit coupled
small polarons. It is shown that effects of an in-plane electric field on a
homogeneous spin system can completely be described by an associated in-plane
magnetic field. Exploiting this analogy, we predict among other things the
electric-field equivalent of the Hanle effect.
