Direct and reversible holographic recording of surface-relief gratings in ate-dye polymers was recently evidenced using atomic force microscopy. Irradiation with an interference pat trm between polarized laser beams was observed to lead to quantitative mass-transport. The surface gratings have a negative amplitude that can be twice as large as the polymer film thickness, The origin of such photo-driven mass transport is still controversial. We provide here experimental evidence that the chromophores migrate from the high to low the intensity regions. Chain migration in such doped or grafted guest-host polymer systems results from the photoinduced migration of the guest chromophores.