  A general formula for the current through a disordered
normal--superconducting junction is derived, which is valid at finite
temperature and includes the full voltage dependence. The result depends on a
multichannel scattering matrix, which describes elastic scattering in the
normal region, and accounts for the Andreev scattering at the NS interface. The
symmetry of the current with respect to sign reversal in the subgap regime is
discussed. The Andreev approximation is used to derive a spectral conductance
formula, which applies to voltages both below and above the gap. In a case
study the spectral conductance formula is applied to the problem of an NINIS
double barrier junction.
