  Spin-conserving and spin-flip opaque reflections of electrons from a
potential barrier in heterostructures are described. An electric field of the
barrier is considered to be the only source of energy spin splitting in the
presence of spin-orbit interaction and its form is calculated in the
three-level {\kp} model for a nontrival case of unbound electrons. Reflection
angles and amplitudes are calculated for oblique incoming directions. It is
shown that the system can serve as a source or filter of spin-polarized
electron beams. Two unexpected possibilities are pointed out: a) non attenuated
electron propagation in the barrier whose height exceeds the energies of
incoming electrons, b) total reflection of electrons whose energies exceed
barrier's height.
