  We study the relevance of the energy correlation produced by the two-body
spin-orbit coupling present in realistic nucleon-nucleon potentials. To this
purpose, the neutron matter Equation of State (EoS) is calculated with the
realistic two-body Argonne $v_8'$ potential. The shift occuring in the EoS when
spin-orbit terms are removed is taken as an estimate of the spin-orbit
correlation energy. Results obtained within the Bethe-Brueckner-Goldstone
expansion, extended up to three hole-line diagrams, are compared with other
many-body calculations recently presented in the literature. In particular,
excellent agreement is found with the Green's function Monte-Carlo method. This
agreement indicates the present theoretical accuracy in the calculation of the
neutron matter EoS.
