  We study the Schr\"odinger operator on $L_2(\mathbb R^3)$ with periodic
variable metric, and periodic electric and magnetic fields. It is assumed that
the operator is reflection symmetric and the (appropriately defined) flux of
the magnetic field is rational. Under these assumptions it is shown that the
spectrum of the operator is absolutely continuous. Previously known results on
absolute continuity for periodic operators were obtained for the zero magnetic
flux.
