  We consider the spin response of a normal Fermi liquid with noncentral
interactions under conditions intermediate between the collisionless and
hydrodynamic regimes. This problem is of importance for calculations of
neutrino properties in dense matter. By expressing the deviation of the
quasiparticle distribution function from equilibrium in terms of eigenfunctions
of the transport equation under the combined influence of collisions and an
external field, we derive a closed expression for the
spin-density--spin-density response function and compare its predictions with
that of a relaxation time approximation. Our results indicate that the
relaxation time approximation is reliable for neutrino properties under
astrophysically relevant conditions.
