  We calculate the Hall transport in a multiband systems with a dominant
interband interaction between carriers having electron and hole character. We
show that this situation gives rise to an unconventional scenario, beyond the
Boltzmann theory, where the quasiparticle currents dressed by vertex
corrections acquire the character of the majority carriers. This leads to a
larger (positive or negative) Hall coefficient than what expected on the basis
of the carrier balance, with a marked temperature dependence. Our results
explain the puzzling measurements in pnictides and they provide a more general
framework for transport properties in multiband materials.
