  We present fluctuation relations that connect spin-polarized current and
noise in mesoscopic conductors. In linear response, these relations are
equivalent to the fluctuation-dissipation theorem that relates equilibrium
current--current correlations to the linear conductance. More interestingly, in
the weakly nonlinear regime of transport, these relations establish a
connection between the leading-order rectification spin conductance, the spin
noise susceptibility and the third cumulant of spin current fluctuations at
equilibrium. Our results are valid even for systems in the presence of magnetic
fields and coupled to ferromagnetic electrodes.
