  We present a description of spin-polarized transport in mesoscopic
ferromagnet-superconductor (F/S) systems, where the transport is diffusive, and
the interfaces are transparent. It is shown that the spin reversal associated
with Andreev reflection generates an excess spin density close to the F/S
interface, which leads to a spin contact resistance. Expressions for the
contact resistance are given for two terminal and four terminal geometries. In
the latter the sign depends on the relative magnetization of the ferromagnetic
electrodes.
