  We propose an experiment, which would allow to pinpoint the role of
spin-orbit coupling in the metal-nonmetal transition observed in a number of
two-dimensional systems at low densities. Namely, we demonstrate that in a
parallel magnetic field the interplay between the spin-orbit coupling and the
Zeeman splitting leads to a characteristic anisotropy of resistivity with
respect to the direction of the in-plane magnetic field. Though our analytic
calculation is done in the deeply insulating regime, the anisotropy is expected
to persist far beyond that regime.
