  Quasiclassical boundary conditions for electrochemical potentials at the
interface between diffusive ferromagnetic and non-magnetic metals are derived
for the first time. An expression for the boundary resistance accurately
accounts for the momentum conservation law as well as essential gradients of
the chemical potentials. Conditions are established at which spin-asymmetry of
the boundary resistance has positive or negative sign. Dependence of the spin
asymmetry and the absolute value of the boundary resistance on the exchange
splitting of the conduction band opens up new possibility to estimate spin
polarization of the conduction band of ferromagnetic metals. Consistency of the
theory is checked on existing experimental data.
