  Weyl semimetals are three dimensional analogs of graphene where the energy of
the excitations are a linear function of their momentum. Pyrochlore Iridates
$(A_{2}Ir_{2}O_{7})$ with A =yttrium or lanthanide element) are conjectured to
be examples of such a system, with the low energy physics described by twenty
four Weyl nodes. An intriguing possibility is that these materials provide a
physical realization of the Adler-Bell-Jackiw anomaly. In this letter we
investigate the properties of pyrochlore iridates in an applied magnetic field.
We find that the dispersion of the lowest landau level depends on the direction
of the applied magnetic field. As a consequence the magneto-conductivity in an
electric field, applied parallel to the magnetic field is highly anisotropic,
providing a detectable signature of the semi-metallic state.
