  Current noise provides useful information on correlations important for
transport properties of mesoscopic systems. Of particular interest, both
experimentally and theoretically, are heterostructures of normal metals and
superconductors. We use an extended Keldysh-Green's function approach to
calculate the current correlations fully accounting for the superconducting
proximity effect. The shot noise in diffusive wires shows a reentrant
behaviour, similar to the reentrance effect of the conductance. At intermediate
energies the effective charge (the ratio of the differential noise and
differential conductance) is suppressed below the value of the Cooper pair
charge 2e due to higher correlations. In superconducting heterostructures with
more than two normal leads, we address the question of the sign of correlations
between currents in different terminals. We show that positive
crosscorrelations are a generic feature in these structures, which should be
easily observable experimentally.
