  We present a study of transport properties of the heavy fermion URu$_2$Si$_2$
in pulsed magnetic field. The large Nernst response of the hidden order state
is found to be suppressed when the magnetic field exceeds 35 T. The combination
of resistivity, Hall and Nernst data outlines the reconstruction of the Fermi
surface in the temperature-field phase diagram. The zero-field ground state is
a compensated heavy-electron semi-metal, which is destroyed by magnetic field
through a cascade of field-induced transitions. Above 40 T, URu$_2$Si$_2$
appears to be a polarized heavy fermions metal with a large density of carriers
whose effective mass rapidly decreases with increasing magnetic polarization.
