A formalism is described to provide the evolution of the polarization of probing radiation propagating in magnetized plasma where retroreflection is used. It is found that when the retroreflector involves an odd number of reflections, such as occurs in the cube-corner retroreflector, both the Faraday and the Cotton–Mouton effects are additive. However, only in special cases are the effects of the double crossing twice those of a single crossing.