  We present calculations of quantized conductance and magnetoresistance in
nanosize point contacts between two ferromagnetic metals. When conductance is
open for only one conduction electrons spin-projection, the magnitude of
magnetoresistance is limited by the rate of conduction electron spin-reversal
processes. For the case when both spin-channels contribute to the conductance
we analyze the influence of the point contact cross-section asymmetry on the
giant megnetoresistance. Recent experiments on magnetoresistance of magnetic
point contacts are discussed in the framework of the developed theory.
