  It is well--known that when magnetic monopoles are introduced in plasma
equations the propagation of electromagnetic waves is modified. This occurs
because of Maxwell equations acquire a symmetrical structure due to the
existence of electric and magnetic charge current densities. In this work we
study the nonlinear phenomena of ponderomotive forces associated to the
presence of magnetic monopoles in a plasma. We generalize the Washimi-Karpman
result for the ponderomotive force on electric charges to take into account the
symmetrical form of Maxwell equations in the presence of magnetic charges. It
is shown that the general ponderomotive force on this plasma depends
non--trivially on the magnetic monopoles, through the slowly temporal and
spatial variations of the electromagnetic field amplitudes. The magnetic
charges introduce corrections even if the plasma is unmagnetized. This last
force induces a magnetization of the plasma, and therefore a cyclotron
frequency (proportional to the square of the magnetic charge) is induced for
electrons. Finally, the magnetic monopoles also experience a ponderomotive
force due to the electrons. This force accelerates the magnetic charges along
the direction of propagation of the electromagnetic waves. The possible
consequences for experimental detection are discussed.
