  We analyze the spinodal instabilities of spin polarized asymmetric nuclear
matter at zero temperature for several configurations of the neutron and proton
spins. The calculations are performed with the Brueckner--Hartree--Fock (BHF)
approach using the Argonne V18 nucleon-nucleon potential plus a three-nucleon
force of Urbana type. An analytical parametrization of the energy density,
which reproduces with good accuracy the BHF results, is employed to determine
the spinodal instability region. We find that, independently of the of the
orientation of the neutron and proton spins, the spinodal instability region
shinks when the system is polarized, being its size smaller smaller when
neutron and proton spins are antiparallel than when they are oriented in a
parallel way. We find also that the spinodal instability is always dominated by
total density fluctuation independently of the degree of polarization of the
system, and that restoration of the isospin symmetry in the liquid phase, {\it
i.e.,} the so-called isospin distillation or fragmentation effect, becomes less
efficient with the polarization of the system.
