  We calculate the quantum correction to the classical conductance of a
disordered mesoscopic normal-superconducting (NS) junction in which the
electron spatial and spin degrees of freedom are coupled by an appreciable spin
orbit interaction. We use random matrix theory to describe the scattering in
the normal part of the junction and consider both quasi-ballistic and diffusive
junctions. The dependence of the junction conductance on the Schottky barrier
transparency at the NS interface is also considered. We find that the quantum
correction is sensitive to the breaking of spin rotation symmetry even when the
junction is in a magnetic field and time reversal symmetry is broken. We
demonstrate that this sensitivity is due to quantum interference between
scattering processes which involve electrons and holes traversing closed loops
in the same direction. We explain why such processes are sensitive to the spin
orbit interaction but not to a magnetic field. Finally we consider the effect
of the spin orbit interaction on the phenomenon of ``reflectionless
tunnelling.''
