  Spin transport properties of a spin-polarized two-dimensional electron gas
are studied in the presence of electron-electron interactions. Longitudinal and
transverse spin diffusion coefficients are calculated with the quantum
transport equation which includes many-particle effects in the random phase
approximation. We find that the $e$-$e$ scattering, which does not contribute
to charge drift mobility, has a significant contribution to the spin diffusion.
Thus, $e$-$e$ interaction causes non-negligible effects on the operations of
proposed devices dependent on spin transport in semiconductor heterostructures.
