  We demonstrate that the variation of the Andreev reflection with applied
magnetic field provides a direct means of comparing the properties of MgB2 with
the theory for a dirty two-band superconductor, and we find good agreement
between the two. The ratio of electron diffusivities in the s and p bands can
be inferred from this experiment. We find that the field dependence of the
density of states at the Fermi level in the p band is independent of the field
direction, and that the anisotropic upper critical field is determined by the
anisotropic diffusivity in the s band.
