  A generalized analysis of the local entropy production of a simple fluid is
used to show that, if intrinsic angular momentum is taken into account,
rotational viscosity must arise in the linear non-equilibrium regime. As a
consequence, the stress tensor of dense rotating matter, such as the one
present in neutron stars, posseses a significant non-vansishing antisymmetrical
part. A simple argument suggests that, due to the extreme magnetic fields
present in neutron stars, the relaxation time associated to rotational
viscosity is large (approx 10^{21} s). The formalism leads to generalized
Navier-Stokes equations useful in neutron star physics which involve vorticity
in the linear regime.
